GB2252639A

GB2252639A - Dynamic tracking system.

Info

Publication number: GB2252639A
Application number: GB9125505A
Authority: GB
Inventors: Chan-Young Park; Kye-Jong Kim
Original assignee: Samsung Electronics Co Ltd
Current assignee: Samsung Electronics Co Ltd
Priority date: 1990-12-29
Filing date: 1991-11-29
Publication date: 1992-08-12
Anticipated expiration: 2011-11-29
Also published as: KR940009171B1; KR920013269A; DE4139188C2; GB2252639B; DE4139188A1; FR2671443B1; GB9125505D0; JP3123793B2; JPH04341914A; FR2671443A1

Description

1 2 2 5 2 I - 1 DYNAMIC TRACKING APPARATUS AND METHOD USING AN ERROR FLAG

SIGNAL This invention relates to a dynamic tracking apparatus and method that uses an error flag (EF) signal, and in particular, relates to a tracking apparatus and method I thereof that uses an error flag signal,of a code-word unit generated due to deviant tracki p in an error correction decoder of a digital tape recorder(hereinafter referred to as D-VIR) reproduction section to enable accurate normal tracking by correcting a position of a piezoelectric device adhering to a drum head.

For tracking in the reproduction seption of the general D-VIR, there have be6n a pilot signal tracking method and a dynamic tracking method. The pilot signal tracking method as illustrated in FIG. 1. uses 4.pilot signals recorded along with the video signal on a video tape in the tracking servo. In the 8mm VTR, these pilot signals are recorded by the video head and are positioned in a zone lower than the color signals. The 4 pilot signals have the frequencies: 102.5KHz for fi, 119.0MIz for f2, 165.2KHz for f3 and 148.7KHz for f4.

Since the frequency differences between the 4 pilot signal frequencies being f2-fifB-f4=16.SKHz and f4-fl=f3f2=46.2Mz, the pilot signal frequencies fi and f4 are 2 sensed when the video head deviates to the f4 track side. When pilot signal frequencies fi and f4 are sensed and the frequency difference f4- fi of the pilot signals becomes the error signal f(46.2KHz), the video head H is made to restore its tracking to the normal fi track immediately. However, when the high density signals such as digital video signals were recorded on a video tape by using this pilot signal tracking method, there was the problem that a certain pilot signal frequency could not be used as one reference frequency during the reproduction with a variable speed because crosstalk between the pilot signal and video signals occurs.

In addition, although a conventional head is fixed to the drum directly, the tracking head in the case of dynamic tracking, is assembled as illustrated in FIG. 2 in;uch a way as to apply a control voltage to. the piezoelectric device b in which the drum is connected to the base a of the device and to cause to displace the head c, which is attached to the piezoelectric device b toward the video tape d. The scope of the possible displacement of head c is limited in view of the machine's structure, for example, with a displacement width of 0.6mm, when the track pitch is 0. 18mm, a 3 track position displacement becomes possible to allow a triplespeed playback reproduction, a still reproduction and a normal speed reverse reproduction.

3 Furthermore, the conventional dynamic tracking method is a method that extracts and synchronously detects an amplitude component from a radio frequency RF signal envelope generated by scanning and oscillating head c connected to piezoelectric device b by about 720Hz and deviates the piezoelectric device b by detecting a tracking direction by a synchronously detected amplitude signal. However, in using the conventional dynamic tracking method to record and reproduce a digital signal, it is not possible to detect the envelope of the RF signal itself and there is the problem of not being able to perform tracking in the system having the accuracy of displacement of head c of the 18im track pitch system.

Therefore. in order to solve the above problems, it is an object of this invention to provide a dynamic tracking apparatus and method thereof using an error flag signal that enables normal tracking by correcting a head position whenever the error flag signal occurs more than the reference value by regularly checking the frequency of the error flag signal occurring during the reproduction process of a video signal recorded on a video track via the head drum o f a D-VIR.

In order to achieve the above stated purpose of the present invention, there is provided a dynamic tracking apparatus comprising a signal reproduction section to 4 receive a signal that has been stored on a video tape in a magnetized condition via a head on a drum and to convert it into an electrical signal; a time base error correction section that reduces jitters included among the signals being reproduced into the electrical signal in the signal reproduction section; a synchronous detector section to distinguish synchronous signals having the certain patterns from among the signals output from the time base error correction section and align the reproduced signals into parallel signals as before being recorded; a first error correction/decoding section that corrects error signals that can be corrected per a code word among the error signals included in the reproduced signals output from the synchronous detection section and generates an error flag signal with respect to the error signals that can't be corrected; a deshuffling section to change burst type error signals output from the first error correction/decoder section into random error signals; a second error correction/decoding section that corrects error signals that can be corrected per a code word among the random error signals output from the deshuffling section, and generates the error flag signal with respect to the error signals that can't be corrected; a multiplexer section that selects and outputs one of the error flag signals transmitted respectively from the first and second error correction/decoding sections according to the mode selection signal; a system controller that compares the error flag signal selected from the multiplexer section with a reference value set in advance to output a control signal when the error flag signal is larger than the reference value; and a head position driver section that outputs a driver signal to the head to change the position of the head by the control signal output from the system controller.

There is also provided a dynamic tracking method using an error flag signal in a tracking control device of a reproduction system that reproduces encoded, compressed digital data, said method comprising the steps of: generating a first error flag signal for an error signal that can't be corrected among burst error signals included in the reproduced signals; deshuffling to change said burst error signals into random error signals; generating a second error flag signal for an error signal that can't be corrected among said random error signals; receiving said first and second error flag signals, and selecting and outputting one of the first and second flag signals according to a mode selection signal; counting said selected error flag signal; comparing the output counted from the error flag signal counting step with a reference value set in advance; and generating a control signal to control a position of a reproduction head by the compared output of 6 the comparing step.

FIG. I shows pilot signals in a tracking servo of a video recorder, FIG. 2 shows a conventional dynamic tracking head, FIG. 3 is a block diagram of a video signal reproducer to which a dynamic tracking apparatus according to the present invention is applied, and FIG. 4 is a circuitry diagram of an video signal selector section as illustrated in FIG 3.

A detailed explanation of the present invention follows with reference to the accompanying drawings.

According to FIG. 3, the respective elements of a video signal reproducer to which the dynamic tracking device of the present invention is adapted will be described below. A signal reproduction section 10 converts a signal stored on a video tape VT in a magnetic condition that is received through a head H of drum D into an electrical signal. A time base error correction section 20 reduces jitter included in the signals that are reproduced as electrical signals in signal reproduction section 10. A synchronous detection section 30 senses synchronous signals having a certain pattern among the output signals of the time base error correction section 20 and arranges the reproduced signals as parallel signals as prior to being recorded. A first error correction/decoding section 40 corrects the 7 error signals that can be corrected per a code word among the error signals included in the reproduced signals in synchronous detection section 30, and generates the error flag signal with respect to the error signals that can not be corrected. A deshuffling section 50 changes burst type error signals output from first error correction/decoding section 40 into random error signals. A second error correction/decoding section 60 corrects the error signals that can be corrected per a code word among the random error signals output from deshuffler 50, and generates the error flag signal with respect to the error signals beyond correction. A multiplexer 70 selects and outputs one of error flag signals being respectively sent from first and second error correction/decoding sections 40 and 60 as determined by a mode selection signal S. A system controller 80 that consists of a counter 81, a comparator 82, an OR gate 83, and a head position control section 84, compares an error flag signal selected in multiplexer 70 with a reference value set in advance and outputs a control signal when the error flag signal is greater than the reference value. A head position driver section 90 outputs a drive signal to head H causing the head H position to be altered as determined by the control signal output from system controller 80. A data interpolator 100 expands the video signal having the quantity of the compressed 8 information output from second error correction/decoding section 60. A video signal switching section 110 outputs a pre-frame video signal received from data interpolator 100 for either the pixel or block in which the error flag signals are generated and for non-error flag video signals, outputs the video signal received from data interpolator 100. A digital/analog signal converter section 120 converts the respective digital video signals output from video signal switching section 110 into analog video signals for transmitting to a monitor set NIS.

An explanation of the operational relationship between the constructional elements having the functions as described above follows.

With reference to FIG. 3, a signal stored in a magnetic state on a video tape VT is converted to an electrical signal in signal reproduction section 10 and transmitted to the time base error correction section 20. Time base error correction section 20 reduces time waver, referred to as jitter due to error in the time base, generated by rotation of drum D, geometric distortion from the head H assembly, and expansion and vibration of the video tape VT and sends the time-base-error corrected signal to synchronous detection section 30. Synchronous detection section 30 detects synchronous signals that have the certain patterns among the signals sent from time base error correction 9 section 20 and arranges those reproduced signals into the parallel signals before being recorded on the video tape VT. Then, first error correction/decoding section 40 corrects error signals that can be corrected per a code word among the parallel signals output from synchronous detection section 30 and generates an error flag signal for other error signals that are not corrected, sending its output to both deshuffler 50 and multiplexer 70. Desbuffler 50 changes burst errors into random errors to improve this system's error correction capability.

In addition, multiplexer 70, which is a 2x1 multiplexer, applies the error flag signals from first error correction/decoding section 40 during the multiplied and reduced speed reproduction to the clock terminal of counter 81 included in the system controller 80 by the mode selection signals by the mode selection signal S, while it applies the error flag signal from second error correction/decoding section 60 during the normal reproduction. The output value of counter 81 is input to comparator 82 and is compared with a reference value set in advance, so that when the output value of counter 81 is of less value than the reference value, head position control section 84 maintains the current bead control operation, but when the output value of counter 81 is more than the reference value, head position control section 84 drives head position drive section 90 to alter the position of the head to control tracking. Then, during the initial period of the head position control which is under the control of software in the head position control section 84, one cycle deviation of the head to the left and right is made to set the head H position to the optimum position that minimizes the number of error flag signals. Then, the clock source of counter 81 becomes the error flag signal that is output through multiplexer 70 and a clear signal becomes applied through OR gate 83 using the output signal of comparator 82 and a vertical synchronous signal V-SYNC.

The video signal output from second error correction/decoding section 60 is sent in a compressed state to data interpolator 100 by which is restored the video signal that existed prior to compression of the information quantity as much as possible.

Next, video signal switching section 110, which contains a frame delay memory, outputs a video signal prior to one frame for pixel or block generating error flag signals and directly outputs the signals received from data interpolator 100 for normal reproduced signals, which produce no error flag signals. Structure of this video signal switching section 110 is illustrated by the circuit diagram in FIG. 4 and operation thereof is represented by the following table.

11 Table Operation of the Video Signal Switching Section m, 1 MUX 2 REMARK OUTUF OUIPL7 ERROR FLAG A=C, A c C is a frame SIGNAL EXIST delayed signal.

ERROR FLAG z B B SIGNAL NION-EXIST A digital video signal that is selected and output from video signal switching section 110 is converted to an analog video signal in digital/analog signal converter section 120 and sent- to the monitor set MS. Then, the frame delay memory contained in the video signal switching section 110 writes the signal being input to the digital/analog signal converter section 120 and uses it as a video signal for an error correction in the next frame.

As described above, the present invention corrects the head position when error flag signals are generated beyond the reference value by periodically checking the frequency of the error flag signals generated and controls the error flag signals less than the reference value to be generated, thereby performing normal tracking.

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Claims

1. A dynamic tracking device using an error flag signal for use in a reproduction system of a digital video tape recorder, said device comprising: a signal reproduction section (10) that receives a signal stored on a video tape in a magnetic state through a head on a drum and converts it into an electrical signal; a time base error correction section (20) that reduces jitters included among signals reproduced as the electrical signals in said signal reproduction section (10); a synchronous detection section (30) that senses synchronous signals having the certain patterns from among signals output from said time base error correction section (20) and arranges the reproduced signals into parallel signals as prior to being recorded; a first error correction/decoding section (40) wherein among error signals included in the reproduced signals output from said synchronous detection section (30), the error signals that can be corrected per a code word are corrected and error flag signals are generated for the other error signals: a deshuffler (50) section that changes burst type error signals output from said first error correction/decoding section (40) to random error signals; 13 a second error correction/decoding section (60) that corrects error signals that can be corrected per a code word among the random error signals output from said deshuffler section (50) and generates an error flag signal for the other error signals; a multiplexer (70) that selects and outputs one of error flag signals sent from said first and second error correction/decoding sections (40 and 60) according to a mode selection signal; a system controller (80) that compares the error flag signal selected in said multiplexer (70) with a reference value set in advance. and when the error flag value is greater than the reference value, outputs a head position control signal; and a head position drive section (90) that outputs a drive signal to the head to alter the position of the head as directed by the said head position control signal output from said system controller (80).

2. A dynamic tracking device as claimed in claim further comprising: a data interpolator section (100) that expands the video signal having a compressed information quantity output from said second error correction/decoding section (60); a video signal switching section (110) that receives and outputs a video signal prior to certain frames from an 14 internal frame memory for pixels or blocks where error signals are generated and receives the video signals said data interpolator (100) to directly output the signals which do not generate error flag signals; a digital/analog signal converter section converts respective digital video signals output from video signal switching section (110) into analog signals and sends the output to a monitor set, f lag f rom video and (120) that said video whereby said dynamic tracking dev ice is adapted to a video signal reproduction circuit for a normal tracking.

3. A dynamic tracking device as claimed in claim 1, wherein said system controller (80) comprises: a counter (81) that receives and counts output from said multiplexer (70); the signals a comparator (82) that receives and compares the output value counted from said counter (81) with a reference value set in advance; and a head position control section (84) that outputs a control signal when the output value from said counter (81) becomes greater than the reference value set in advance in said comparator (82).

1

4. A dynamic tracking device as claimed in claim 3, wherein said counter (81) becomes initialized as directed by a logical combination of the output of said comparator (82) and a vertical synchronous signal.

5. A dynamic tracking device as claimed in claimed 2, wherein said video signal switching section (110) comprises: a frame delay memory that delays the output signal of said data interpolator (100); a second multiplexer (NM, 2) that selectively outputs a signal from said data interpolator (100) or a signal from said frame delay memory according to an error flag signal from said second error correction/decoding section (60); and a first multiplexer (NW 1) that selects an output signal from said second multiplexer (N= 2) or an output signal from said data interpolator section (100) according to the error flag signal from said second error correction/decoding section (60) and provides the selected signal to store in said frame memory.

6. A dynamic tracking method using an error flag signal in a tracking control device of a reproduction system that reproduces encoded, compressed digital data, said method comprising the steps of: generating a first error flag signal for an error signal that can't be corrected among burst error signals included in the reproduced signals; deshuffling to change said burst error signals into 1 16 random error signals; generating a second error flag signal for an error signal that can't be corrected among said random error signals; receiving said first and second error flag signals, and selecting and outputting one of the first and second flag signals according to a mode selection signal; counting said selected error flag signal; comparing the counted output from said error flag signal counting step with a reference value set in advance; and generating a control signal to control a position of a reproduction head by the compared output of said comparing step.

7. A dynamic tracking method as claimed in claim 6, further comprising a step of driving a head position driving section according to said control signal output from said control signal generating step.

8. A dynamic tracking apparatus and method using an error flag signal substantially as hereinbefore described with reference to FIG. 3 of the accompanying drawings.

9. Apparatus for adjusting the relative position of a read head and a digital data storage medium comprising error detection means, and control means responsive to said error detection means for acting on said read head or storage medium thereby to adjust their relative positions in order to minimise the rate at which errors are detected thereby.

10. Apparatus as claimed in claim 9, wherein the error detection means comprises a first error detection circuit and a second error detection circuit, said first and second error detection circuits being operable to detect errors in the data read by said read head in respective different manners, wherein the control means is made responsive to either the first or the second error detection circuit in accordance with a mode selection input signal, said mode selection signal corresponding to the relative speed of the read head and storage medium.