KR840001432B1 - Video disc apparatus for clearing foreign matter from the signal pickup stylus during playback - Google Patents

Abstract

Accmulated foreign material on the signal pickup stylus of a video disc player tends to degrade the quality of the recovered information signal. The recovered information signal is detected and the nominal ampitude of the recovered signal is compared against a reference amplitude. The occurrence of a decrease in recovered signal amplitude below the level of the reference cause a comparator to generate a control or trigger pulse. The control pulse activates a pulse generator to produce a predetermined pulse sequence which is applied to a stylus deflection transducer to move the sylus fore and aft radially across the disc and thereby dislodge the foreign material from the picku stylus.

Description

Video disc device for erasing foreign matter from signal pick-up needle during playback

1 and 6 show partial schematics and schematics embodying different systems for deriving needle alternators in response to signal amplitude reduction and data errors.

2 is a circuit diagram for generating a control signal responsive to a reduced signal amplitude occurring over a defined period of time.

3 is a circuit diagram for generating a pulse train in response to a control pulse transition.

4 is a circuit diagram for driving a pickup needle knitting machine converter.

5 is a waveform diagram of potentials occurring at various places in the circuits of FIGS.

7 is a flow diagram illustrating the operation of the FIG. 6 circuit.

8 is a graph of memory error values calculated from one flow chart in FIG.

6 is a schematic diagram of a system for leaking a digital confirmation signal from a reproduced video signal.

The present invention relates to video disc playback systems and, more particularly, to an apparatus for erasing foreign matter accumulated from a signal pickup needle to be reproduced.

Certain video disc systems use disc records that have information recorded in geometric variations along the signal track. The recorded information is reproduced from the disc record by the revolving needle engaged with the disc record when a relative motion occurs between the needle and the disc by rotating the disc. These needle-disc playback systems exist in many forms, such as some systems that use grooved disc records, for example, where the pick-up needle is pressed to follow the information track by the groove walls, while other systems have information about the pick-up needle. Uses grooveless records held closest to the information track by a drive system responsive to tracking information recorded on a record adjacent to the track. There are many different types of slotted disc systems. This first type of dose systems responds to a change in volume between the needle and the disc record, whereas the second type, pressure sensing systems, is subject to geometric changes in the groove perpendicular to the direction of relative velocity between the needle and the disc. Signals are generated as a result of movement induced in the needle.

Each of the above mentioned types of systems has reduced functionality due to the accumulation of foreign matter on the pick-up needle. The debris can be dust, moisture, residues from disc wear after repeated play, etc. and they try to adhere to the needle. This accumulation of foreign matter impedes the needle's ability to track in slotted disc systems, adversely affects the relative needle-disc capacity in capacitive pick-up systems, and in geometrical changes in pressure sensing systems. Thereby reducing the movement induced in the needle. The final adverse effect is an unnecessary reduction in the reproduction of the error data when the recorded information in the video display form and the disc are used for data purposes. It is desirable to remove debris from the pick-up needle with minimal regeneration interruption without visually interrupting the video display.

According to the present invention, a signal reproduced from a disc record is detected to detect specialized signal reductions so that when the specialized signal reduction occurs, the needle drives the transducer to skip back and forth across some information track on the disc radially. Let's do it. Sudden changes in the needle, as well as increased pressure and abrasion between the needle and the disc, which are common to needle skipping, tend to erase and desorb accumulated foreign material from the needle, thus allowing for a modified signal level. Re-remember to Radial skipping back and forth not only causes the needle to return to the position closest to the first knitting point, but also causes the memory to be removed from the needle. Pick-up needle knitting machines can be conditioned to occur during video vertical erase periods so that playback indications will not be disturbed. Hereinafter, with reference to the accompanying drawings will be described in more detail.

In FIG. 1, carriage assembly 10 supports and carries signal pick-up needle 14 over disc record 9. As shown in FIG. The pick-up needle 14 is engaged with the disc record through the hole 8 of the carriage and the carriage is carried by the synchronizer 11. The pick-up needle 14 is mounted to the free end of the rigid needle arm 12 and the second end of the needle arm 12 is fixed to the carriage by a flexible connector 13. The connector 13 allows relatively free movement of the pickup needle at least in the direction of movement of the carriage, indicated by V in the figure.

A transducer for inducing the movement of the needle in relation to the carriage and the disc record is included in the carriage assembly. The transducer is illustrated in FIG. 1 with a pair of coils 15 fixed to the carriage assembly on both sides of the needle arm. Magnetic element 7 is fixed to the needle arm and is disposed between the coils 15. By driving the coils as a current flowing through the conductor 23, sufficient magnetic flux is generated to move the element 7 in the region between the coils, so that the needle arm 12 and the needle 14 to which the element 7 is fixed are knitted. The knitting direction of the needle is determined by the curvature of the applied driving current.

The pickup needle 14 cooperates with the disc record 9 and the signal pick-up circuit 16 to reproduce the information previously recorded on the disc. For an example of capacitive form video disk systems, see J. K. Clemens' RCA Video Capacity Pickup and Acquisition Code System, pages 33 to 59 of RCA Review Magazine 39, March 1, March 1978, and March 21, 1978. See US Pat. No. 4,080,625 to Kawamodo et al., Titled Pickup Circuit for Video Disc Players with Printed Circuit Boards, assigned to RCA Corporation. The reproduction signals extracted from the pickup circuit 16 at the contact point 22 are set by the audio and video processing circuit 17 for application to the antenna input terminals of the conventional television receiver 18.

The signal extracted at contact 22 can be amplitude, phase or frequency modulated depending on the particular system. For illustrative purposes a capacitive disk system will be assumed and the signal at contact 22 will be assumed to have a constant rated amplitude and to be frequency modulated, ie FM. Accumulation of foreign matter on the pick-up needle attempts to reduce the disc-needle absolute capacity, which leads to disc-needle capacity changes at the moment of indicating the recorded information. This reduction in instantaneous capacitance changes is confirmed by a decrease in the amplitude and quality of the FM signal.

The signal at contact 22 is applied to circuit 19 and detected by, for example, a peak detector and then compared against a reference potential. The output signal from circuit 19 indicates a transition to control circuit 20 when the detected signal falls below a predetermined reference fixed to a few percent of the detected rated amplitude.

The detection circuit described above permits systems with very constant mutual disk-needle parameters, i.e., the signal amplitude at 22 gradually does not change significantly when the disks or needles are interchanged and the signal amplitude allows constant systems across each disk. can do. However, it is recognized that the amplitude can be changed to 10: 1 for disk-needle interchange. This change precludes the use of one fixed criterion to compare the detected signals. Therefore, circuit 19 applies automatically to the rated amplitude of each needle-disk coupling and needs to detect the relative changes in signal amplitude.

The circuit shown in FIG. 2 detects the signal amplitude applied to the input terminal 22 'and self-adjusts to produce a potential transition at the output terminal 24' in response to a predetermined average amplitude reduction that lasts for a predetermined period of time. In the circuit, transistor 33 is connected as an emitter follower. The signal potential applied to the base electrode is transferred to the emitter electrode with a smaller base-emitter forward potential drop. Resistors 31 and 32 bias the base of transistor 33 to some value such that the AC signal appearing at input 22 'affects the emitter current of transistor 33. Capacitor 30 isolates the base electrode from the DC potential of terminal 22 'and applies AC signals from terminal 22 to the base of the transistor. Consider a circuit in which an FM signal of a stable state, that is, a constant rated amplitude, is applied to an input terminal. The positive peaks of the FM signal forward balance the base emitter junction of transistor 33 to charge capacitor 34. Negative vibration of the FM signal reverse biases the base-emitter junction and transistor 33 is turned off. In all negative half-cycles of the FM signal, the charge of capacitor 34 begins to discharge through the leakage, or resistance 35, and the potential at the emitter electrode is reduced to a time constant determined by the resistance and capacitance values of R35 and C34, 35 and 34, respectively. do. Since the resistance of the resistor 36 is larger than that of the resistor 35, the current flowing through the resistor 36 is not large. Since the time constants R35 and C34 are longer than the cycle time of the input FM signal, a small percentage of charge flows out of the capacitor during each negative half period of the input signal, and the potential at the emitter electrode is approximately at the peak level of the input signal. Thus, the combination of emitter-base junction and resistor 35-capacitor 34 performs amplitude detection.

If the amplitude of the input signal decreases by an amount greater than the potential drop on the capacitor associated with the negative half period, successive signal peaks will be insufficient to forward bias the base-emitter junction of transistor 33 and capacitor 34 will have The discharge will continue until the level drops below the base-emitter potential drop below the peak input signal and the potential of the emitter will stabilize at this level. The potential level at the emitter can easily follow the increase in the input signal amplitude but is pressed to follow the decrease at the rate set by the R35 and C34 time constants.

Resistors 36 and 38 form a voltage divider that divides the voltage provided to the emitter by the ratio of (R38 + R36), where R38 and R36 are the resistance values of resistors 38 and 36, respectively. This voltage is applied as the reference potential to the non-inverting input terminal r of the differential amplifier 39. The capacitor 37-resistance 38 coupling sets the reduction ratio to r, which is a longer ratio than the time constants R35 and C34 associated with the emitter electrode of transistor 33 during the negative potential changes. The potential of the reduction ratio r is late in response to changes in the emitter potential and sets the nominal reference level depending on the input signal level of the long needle, i.e. the specific needle-disk combination. This is a self-adjusting or automatic reference generation feature.

The inverting input terminal r of the differential amplifier 39 is connected to the emitter of the transistor 33 so that it follows the average peak signal applied to the input 22 '. Referring to FIG. 5, waveform A is an FM signal whose amplitude is likely to decrease and is applied to the base of transistor 33 through terminal 22 '. This signal is commutated, detected by the transistor base-emitter junction, and appears on the emitter as a slowly changing DC signal (waveforms B and C are shown enlarged in the figure). The emitter potential decreases to a new, smaller peak amplitude because the R35 and C34 time constants cannot follow abrupt negative changes in the A signal amplitude over short periods of time. However, the potential reduction at the emitter is much faster than the reduction at terminal r (time T ₁ ) so that the inverting input terminal F of amplifier 39 becomes more negative than the non-inverting input terminal r of amplifier 39 and therefore the amplifier at terminal 24 '. The output potential oscillates from negative saturation to positive saturation, whereby a control signal is generated.

Referring again to FIG. 1, control pulses from circuit 19 are applied to pulse generator 20. FIG. The pulse generator 20 generates a series of pulses selected to cause alternating knitting of the needle 14 by the knitting converter. The output pulse train from generator 20 is applied to buffy / driver 21 to relax and / or adjust the waveform for application to the knitting wall ventilation.

It is advantageous to include a device which blocks the selected pulse train once the signal decay has been eliminated, ie after the minimum number of pulses. This can be achieved, for example, by using a control signal that inhibits the pulse generator after the control signal has returned to its normal state and after the predetermined minimum number of pulses have occurred. It is also beneficial to prohibit the corrective operation after the selected maximum number of pulse trains because it is impossible to eliminate the foreign matter or signal loss is largely due to other causes.

In the illustrated embodiment where the converter comprises a magnetic element between a pair of coils, a bias in the alternating direction is generated by applying a current in the opposite direction to the coil. However, in the relaxed state, in which the transducer does not work, no current biasing the magnet flows through the coils. 4 shows a bridge-type driver circuit that can direct current of any polarity through the converter coils 23 and to prevent current from flowing in the coils during non-scheduler periods. In FIG. 4, signals from gate G ₅ at contact P ₁ are applied to transistor T ₄ and supplemental signals at P ₁ are applied to compensation transistor T ₁ . The logic ″ high ″ at P ₁ will cause two T ₁ and T ₄ to conduct a current going in the direction from point P ₅ to point P ₆ through the converter coils 23. The logic ″ low ″ at P ₁ causes the two transistors T ₁ and T ₄ to be biased off. Similarly, logic ″ high ″ at contact P ₂ will cause transistors T ₂ and T ₃ to conduct current through coils 23 in the direction from point P ₆ to point P ₅ and logic ″ low ″ at P ₂ Will bias the transistors T ₂ and T ₃ . Gates G ₅ , G ₆ and G ₇ are increasingly arranged such that only one of P ₁ or P ₂ is logical ″ high ″ at a particular time. Gate G ₆ (G ₅ ) will provide logic ″ high ″ at output terminal P ₂ (P ₁ ) only while high logic is applied simultaneously to its own two input terminals. Therefore, when the input marked DIR is ″ high ″ and the ″ high ″ pulse appears at the terminal labeled DEF, the logic state at P ₂ will be ″ high ″ simultaneously with the pulse. Note that gate G ₇ is a simple inverter that supplements the logic signal at terminal DIR and applies signal to gate G ₅ . Therefore, two G ₅ and G ₆ cannot simultaneously have logic signal ″ high ″ on two input terminals of each of them. Referring to FIG. 5, the waveform F applied to the DIR terminal and the waveform G applied to the DEF terminal will provide a pulse train waveform H at P ₂ and a pulse train waveform I at P ₁ . . For example, at time T ₂ , if the logical state of DIR is ″ low ″, output P ₂ of gate G ₆ should be ″ low ″. However, gate G ₇ supplements the DIR signal such that the first input terminal of gate G ₅ is ″ high ″ and at the same time the DEF signal is ″ high ″ which satisfies the condition that output terminal P ₁ of gate G ₅ is ″ high ″. to be. Waveforms H and I, respectively occurring at P ₂ and P ₁ , cause the pairs of transistors, T ₁ , T ₄ and T ₂ , T ₃ to alternately challenge and alternately jump back and forth, i.e. on-radiation An electric current flows alternately through the converter coils in opposite directions to guide the knitting of the needle into the directional passage.

Specific pulse trains, shown by waveforms F and G, are generated by the FIG. 3 circuit. In FIG. 3, gates G ₃ and G ₄ interconnected with resistors 43 and 44 and capacitor 45 are selected at contact 46 in response to a monostable harmonic oscillator, i.e., a pulse having an arbitrary duration at input 24 '. One-shot to generate a single pulse of a predetermined duration. The pulse applied to contact 46 may be a non-stable multiharmonic oscillator with gates G ₁ , G ₂ , resistors 40, 41 and capacitor 42 required number of pulses at contact 49, for example waveform E of FIG. 5. Set the state of free oscillation for as long as necessary to provide. This waveform is counted down, or divided into two, by circuit 47 and applied as waveform F to the output terminal labeled DIR. The signal at contact 49 is simultaneously delayed by circuit 48 and applied as a waveform G to the output terminal indicated by DEF. The signal at contact 49 is delayed to position certain DEF pulses into a position ie center into specific DIR pulses. For a detailed description of the operation of monostable and unstable harmonic oscillator circuits, see J. a. See Dean et al. ″ Unstable and Monostable Oscillators Using RCA COS / MOS Digital Integrated Circuits ″, RCA Applications ICAN-6267, 1977, RCA COS / MOS Integrated Circuits Data Book, pages 623-626 of SSD250.

The constant disc record system includes track confirmation information interspersed with previously recorded information. This information is typically encoded in digital form and occurs closest to the vertical erase sync signals for each video field or each video field or each video stored on the disc. These signals, or if present, can be used to determine the signal reduction to begin the needle removal process. The system of FIG. 6 includes a device for determining when an unacceptable number of error digital identification numbers have occurred on a given time substrate, in accordance with this determination, the device knitting the needle as in the aforementioned amplitude detection system. Provide a control pulse to generate pulses for In FIG. 6, circuit elements 51, 53, 54, 56 and 57 correspond to elements 16, 17, 18, 20 and 21, respectively, in FIG. The element 63 extracts digital information from the reproduced signal and applies this information to, for example, the digital processing circuit 60, which is a microprocessor. The digital processing circuit compares the last number with the previous number to determine whether the number is correct last or wrong, and to respond to the generation of the selected number of error checking numbers by triggering the pulse train generator 56. For example, consider a video disc in which information is recorded in NTSC format with generally vertical and horizontal erase periods. Normally, the first 21 horizontal lines of each display field do not contain usable video information, so these parts of the chapter can be used to contain track identification information. If there is more than one chapter per track, ie per line, and if the chapters are arranged in a radial line from track to track, each track length can contain two pieces of information: track and sector. As an example, consider a record disc with a spiral groove with eight chapters per line, and the lines from line to line are aligned in eight 45 ° sectors. The lengths of the lines can be identified successively by three bit digital codes and the lines can be numbered consecutively by another digital code. It is possible to determine whether a probable error occurs by simply checking whether a particular identification number, including the line number and chapter or sector number, follows the normal procedure. A microprocessor equipped with a suitable memory that can store a series of numbers per reproduced identification number to determine if an error occurs in the signal regeneration, and to make some comparisons, is suitable for this task. However, computational circuit 60 does not have to use a microprocessor.

It is not desirable to trigger the needle erase sequence for the detection of a single error because the error may be anomalous rather than the result of signal loss. It is undesirable to require that a certain number of consecutive errors occur before starting the needle operation. This is because the reproduced image may not be allowed before needle operation occurs. The onset of needle erase according to the average number of errors for a given number of possible errors gives a better reproduced video representation. The specific mean function, which is conveniently supplemented to a system based on a microprocessor, is given by the formula:

Where A _n is a single calculated discrete digital function representing the weighted average error signal for each successively sampled data set from which time data has been read, A _n-1 is the function value calculated during the preceding data reading, and K is scaling Element, E is 1 if the confirmation number is incorrect, and 0 otherwise. FIG. 8 is a graph of the function for the case of successive errors (1s) and alternating errors (1-0-1, etc.) with an assigned 15 value scale element K. FIG. Given a system with a threshold of K = 15 and 55 and all video fields have a single identification number, the control pulse will be approximately 0.1 seconds for successive errors and approximately 0.3 seconds for alternate errors.

The series of cases repeated by the microprocessor (μPC) to generate a control pulse to initiate needle removal is shown in the flow chart in FIG. When the system is running, the flow rate starts at the current needle position and A _n-1 is the assigned value. The μPC warns (71) that a confirmation number will appear to indicate reading the number. The number is checked for possible errors (72) and if an error is detected, E is assigned a value of 73 (73) otherwise it becomes a value of 74 (74). The function A _n is calculated (76) as the resultant value compared with the selected threshold ″ T ″. If A _n is greater than or equal to the threshold, a check is made to see if the system is already in needle removal or if it is forbidden to prevent the needle from under the control of any other system. This state can exist if the player is in the form of a quick scan, i.e. reverse play. If A _n is less than or greater than ″ T ″ and the system is in prohibition mode, μPC is a predefined indirect management function with the system whose parameters are not specified when the successive confirmation number is retrieved and the auxiliary functions return to reading mode. 77). If A _n is greater than or equal to ″ T ″ and there is no system prohibition, a control pulse is generated to trigger pulse train generator 56 (82) or μPC can be planned to generate a pulse train directly (83) and pulse train to buffer / driver 57 Is applied. Note that the aforementioned distributions have been arbitrarily chosen for illustrative purposes.

9 shows an apparatus for preforming the extraction of digital information from a reproduced signal. The operation of the device is as follows. Again assume that the digital acknowledgment signal, which is usually written in NTSC form and contains an N-bit sign followed by the M-bit chapter acknowledgment number, appears on the 17th horizontal line of each chapter. The M bit field identification number identifies the track line and sector and the N bit identification code is used to alert the system that consecutive M bits contain useful data, eg track numbers. It is assumed that the maximum bit rate is the same as the fundamental system frequency, such as the color burst frequency, and is synchronous. Clock 90 oscillates at a substantially constant frequency, such as the required fundamental frequency, and also oscillates in synchronization with the fundamental frequency and has an output signal suitable for driving a logic circuit. The demodulated video signals from the video processor are applied to the clock generator 90 through the contact 64 'and to the threshold detector 91 to synchronize with the clock. The threshold circuit sets a state of a video signal including digital information in a double level signal having logic level amplitudes necessary for applying a signal to the shifting auxiliary storage device 92. The signal from the threshold circuit 91 is applied to the N-bit matching filter 94 through the M-bit serial-parallel shifting auxiliary storage device 92 by the clock signal at the terminal 100. Filter 94 generates a correlating pulse on line 96 when consecutive n bits of the signal applied to filter 94 match the planned recognition signal in the filter. The following M signal bits simultaneously included in the auxiliary storage 92 are track and sector information bits. The M bit information retrieved from the M-parallel output contacts 95 is latched and shaped by a latch circuit 93 in response to the correlated pulses occurring on line 96 for use in the microprocessor, where the correlated pulses are microprocessors that exhibit a clear digital signal. It warns the computing device.

Another method of detecting error strings of track identification numbers to detect a reduction in the reproduced signal may be achieved by merely finding the absence of correlated pulses from the matched filter. The absence of correlated pulses in one of these periods indicates that errors have occurred in the cognitive code since the digital strings occur in regularly spaced periods. Errors in the acknowledgment code may indicate a signal reduction, such as errors in track identification numbers. The detection of errors in the acknowledgment can then be used to generate a control signal for shortening the pick-up needle.

Claims (1)

As described in the text and illustrated in the drawings, the pre-recorded information is reproduced from the disc record by the signal pick-up needle, and during the reproduction, a control signal is provided in the video disc system in which foreign matter is easily accumulated on the signal pick-up needle. A first device responsive to a predetermined decrease in the reproduced information signal for generating, a second device responsive to the control signal to generate a predetermined pulse train, and a signal pick-up needle in a manner of erasing the foreign matter from a pickup needle And a transducer device operatively connected to said pick-up needle for responsive to a selected pulse train to erase the foreign matter from said signal pick-up needle during reproduction.

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