FR2547097A1 - DEVICE FOR DETECTING AND SIGNALING THE PRESENCE OF DUST IN AN INFORMATION EXTRACTION SYSTEM - Google Patents

Abstract

THE PRESENT INVENTION RELATES TO A DEVICE FOR DETECTIONING AND SIGNALING OF THE PRESENCE OF DUST OR OTHER FOREIGN BODIES IN AN INFORMATION EXTRACTION SYSTEM. ACCORDING TO THE INVENTION, THIS DEVICE INCLUDES A MEANS OF DETECTION OF DUST, FOR EXAMPLE A LEVEL 2 LOSS DETECTOR ASSOCIATED WITH A COUNTER 3, WHICH DETECTS AN ABNORMAL STATE OF THE EXTRACTION SIGNAL GENERATED BY READER 1. THE DETECTION SIGNAL OF DUST GENERATED IS THEN PROVIDED TO A MAINTENANCE MEANS, SUCH AS A TIMING CIRCUIT 4 WHICH GENERATES AN OUTPUT SIGNAL FOR A PREDETERMINED PERIOD OF TIME AFTER RECEPTION OF THE DUST DETECTION SIGNAL AND A SIGNALING DEVICE 5 OR IS ACTIVE DEPENDING ON THE STATE OF THE MAINTENANCE OUTPUT SIGNAL 4. FROM THE KIND, A NOISE-FREE RESTITUTION OF THE RECORDED INFORMATION IS POSSIBLE IF THE RECORDING MEDIUM OR THE READING HEAD IS CLEANED WHEN THE RECORDING DEVICE IS CLEANED. SIGNALING INDICATES THE PRESENCE OF DUST.

Description

The present invention relates to a device for detecting and

  signaling the presence of dust or other foreign matter in an information extraction system, and more specifically to a device for detecting dust, which are for example on the recording medium and cause losses of level, and to signal the

  presence of these dusts to the user of the information retrieval system.

  In an information retrieval system, such as a video information playback system and / or sound information system, the presence of dust or other foreign matter on a recording medium, a reading device or a read head causes a temporary absence, that is to say a loss of level, of the HF signal (radio frequency) reading which results in the appearance of a relatively large noise in the image or the As a result, a device for compensating for these level losses is made indispensable in the systems.

  extraction of recorded information.

  In conventional level loss compensation devices, a mean value between the data immediately preceding the occurrence of a loss of level and a data item which immediately follows the level loss is used by the compensation in step. other devices, a datum immediately preceding the level loss or a datum transmitted at a predetermined time before the level loss is used for the compensation However, in all these level-loss compensation devices, if there are dusts present on a long distance for example, it becomes difficult to compensate for the loss of level over such a long period of time. In general, the appearance of a loss of level during such a period of time. of time results in deterioration of the video information and / or the sound information read furthermore, in some cases, a loss of nive Over a long period of time results in a malfunction of the servo control which is intended to adjust the reading position of the information picking apparatus. As a result, it has been found desirable to develop a device that detects and

  indicates the presence of dust so that the user of the information extraction system can drive dust out of the recording medium.

  reading device or otherwise.

  An object of the present invention is the development of a device for detecting and signaling the presence of dust in an information retrieval system, by means of which the user of this traction system can drive off the dust. to allow a better reproduction of recorded video or audio information and to prevent

  in addition to malfunctions of the servo-control.

  To do this, the present invention provides a device for detecting and signaling the presence of dust, which is characterized in that it comprises a dust detection means for detecting abnormal states of the extraction signal and generating a dust detection signal, means for maintaining the dust detection signal, the detected presence of the dust being signaled or indicated from an output signal of the dust detection signal maintenance means. Several embodiments of the present invention will now be described in more detail, but only by way of non-limiting examples, with reference to the accompanying drawings in which: FIG. 1 is a block diagram of a first embodiment of the present invention; device for detecting and signaling the presence of dust, according to the present invention; FIG. 2 is a block diagram of a second embodiment in which an integrator is incorporated in the means for generating the dust detection signal; FIG. 3 is a block diagram of a third embodiment of this device for detecting and signaling the presence of dust in which a reading RF signal envelope is detected; Fig. 4 is a block diagram of a fourth embodiment in which the level of the read RF signal is detected; Fig. 5 is a block diagram of a fifth embodiment in which an envelope of a focus error signal generated by the reading device is detected; Fig. 6 is a schematic block of a sixth embodiment in which the level of the focus error signal and a track error signal are compared to provide the pedestrian detection signal; Fig. 7 is a block diagram of a seventh embodiment in which an error in the information output in the form of encoded data is detected; and Fig. 8 is a block diagram of an eighth embodiment which is in fact the seventh embodiment shown in Fig. 7 in which an integrator is provided to integrate the frequency of the error signals. We will first refer to Figure 1 to describe the first

  embodiment of the device for detecting and signaling the presence of dust according to the present invention.

  As shown in this figure, this first embodiment comprises a reader 1 for picking up a radio frequency (RF) signal component representing information recorded on a recording disk and for outputting an output signal which simultaneously encloses a component of a focus error signal representative of the distance between the point of convergence of the extraction laser beam and the surface of the recording disk and a track error signal component representative of the deflection of the point of impact of the extraction laser beam with respect to the center of the recording track The RF signal component generated by the reader 1 is applied to a level 2 loss detector The level 2 loss detector is designed for example in such a way that a positive pulse and a negative pulse are generated in synchronism with the zero crossing points of the RF signal and that either Either of these pulses is used to trigger a retriggerable monostable multivibrator (hereinafter referred to as r-mmvbr) having a predetermined time constant of 207 ns, for example. This time constant of r-mmvbr substantially matches at the maximum period of the HF signal A disappearance of the signal

  HF for a longer period of time than the predefined period of time causes a reversal of the state of the r-mmvbr output signal.

  As a result, a level loss detection signal consisting of, for example, a negative pulse, can be generated on an output terminal Q of the r-mmvbr. The level loss detection signal thus produced is then supplied to a receiver. Counting circuit 3 The counting circuit 3 is composed of, for example, a binary counter which counts the level-loss signals, a pulse generator intended to generate a pulse train at a constant interval and to apply this train of pulses. pulses on the reset terminal of the binary counter, and a number of interconnected logic gates which are responsive to the output signal of the binary counter and are adapted to generate a high level output signal when the

  count value of the binary counter has reached a predetermined value.

  The counting circuit 3 forms, together with the level 2 loss detector, the dust detection means which delivers as a dust detection signal a high level output signal pro10 from the counting circuit 3, when the level loss appears more than one

  predetermined number of times within the predetermined period of time.

  The dust detection signal is then applied to a timing circuit 4 acting as a means for maintaining this signal. The delay circuit 4 is designed, for example, to generate a high level output signal for a predetermined period of time T 2 after the generation of the dust detection signal. The output signal of the delay circuit 4 is then supplied to a controller. signaling device or indicator 5 which is for example constituted by an electro-luminescent diode The second embodiment of the present invention will now be described with reference to the block diagram of FIG. 2. The configuration of this second embodiment is for FIG. identical to that of the first embodiment shown in FIG. 1, except for the structure of the means for generating the dust detection signal as a function of the number of occurrences of level loss within the predetermined period of time More precisely, this second embodiment comprises the reading apparatus 1, the However, in the case of this embodiment, the level loss detection signal generated by the level 2 loss detector is applied to a level 2 loss detector, the timing circuit 4 and the signaling device 5. Integrator 6 In integrator 6, the level loss detection signal is integrated to produce an output signal whose level is proportional to the frequency of appearance of the nihil loss within the time period. predetermined output signal

2547 '097

  of the integrator 6 is compared to a reference signal in a comparator 7 The level 2 loss detector, the integrator 6 and the comparator 7 together form the dust detection means which generates the level dust detection signal when the number of matches of the level loss signals is greater than the predetermined number during a predetermined unit time period. By applying this dust detection signal to the timing circuit 4, the detection of

  For example, the dust present on the recording medium is indicated in the same manner as in the first embodiment shown in FIG.

  FIGS. 3 and 4 show other embodiments of the device for detecting and signaling the presence of dust according to the present invention. The configuration of these two embodiments is substantially identical to that of the first embodiment shown in FIG. FIG. 1 except for the detection of dust which is carried out by detecting the amplitude variation of the captured RF signal by means of the reading apparatus 1. More precisely, in the embodiment of FIG. HF signal from the reading apparatus 1 is applied to an envelope detector 8 which, for example, consists of an AM detection circuit An output signal of this envelope detector 8 is then compared to a signal When a loss of level occurs, i.e., at the instant when the level of the output signal of the envelope detector 8 becomes lower than the reference voltage. Comparatively, the comparator 9 generates a pulsed output signal whose pulse width corresponds to the period of time during which the level of the output of the envelope detector 8 drops. This pulsed output signal of the comparator 9 is in turn applied to a pulse width detector 10 which is adapted to count a clock signal during the presence of the pulsed signal supplied for the comparator 9 and generates a high level output signal when the count value indicates that the pulse width is greater than a predetermined value The assembly consisting of the envelope detector 8, the comparator 9 and the pulse width detector 10, forms the dust detection means which provides as a signal for detecting dust in timing circuit 4, the high level output signal of the pulse width detector 10, when the level of the envelope signal is dropped due to the absence of the signal the HF continues beyond the predetermined period of time After that the detection of dust is signaled by the signaling device of the

  same way as in the embodiment of Figure 1.

  In the case of the embodiment of FIG. 4, the RF signal coming from the reading apparatus 1 is applied to a level detector 11 which, for example, consists of an alternating rectifier circuit receiving the RF signal, and an integrator circuit for integrating the output signal of the rectifier circuit alternately. Thus, the level detector 11 generates an output signal whose level is proportional to the level of the RF signal and this output signal of the level detector. 11 is applied to a comparator 12 in which the output signal of the level detector is compared to a predetermined reference voltage signal. In this way, the level detector 11 and the comparator 12 form the dust detection means which generates as a dust detection signal, a high level output signal from the comparator 12 and supplies this signal to the timing circuit 4, when the signal output signal level

  Then, the detection of the dust present on the recording medium is signaled by the signaling device in the same manner as in the embodiment of FIG. 1.

  FIGS. 5 and 6 show other embodiments of the device for detecting and signaling the presence of dust according to the present invention, which have the same configuration as the embodiment of FIG. 1 except for the dust detection that is performed by using an error signal generated by the device

reading 1.

  In the embodiment of Fig. 5, a focus error signal generated by the reading apparatus 1 is applied to an envelope detector 13. The envelope detector 13 is adapted to detect an envelope of a component. low frequency of the focus error signal The envelope detector 13 together with the comparator 14 and the pulse width detector 15, the dust detection means which supplies the timing circuit 4 with the output signal of high level of the pulse width detector 15 as a dust detection signal, when the level fall of the low envelope signal of the low frequency component of the focus error signal continues beyond the period predetermined time Then, the detection of the dust present on the recording medium is

  signaled by the signaling device as in the preceding embodiments.

  In the case of the embodiment of FIG. 6, the focus error signal and a track error signal generated by the reading apparatus 1 are compared with each other in a comparator. As a result, the comparator 16 outputs a pulse noise signal 10 when the difference between the level of the focus error signal and that of the track error signal varies abruptly due to the presence of dust on the recording medium The pulse-shaped output signal of the comparator 16 is then applied to a counting circuit 17 which consists for example of the same elements as the counting circuit 3 of the embodiment of FIG. to timing circuit 4 a high level output signal when the number of pulse-like output signals generated by the comparator within a predetermined period of time is greater than a predetermined number. te, the detection of dust is signaled by the signaling device 5 in the same way

  when in the previous embodiments.

  FIGS. 7 and 8 are block diagrams of other embodiments of the device for detecting and signaling the presence of dust according to the present invention, which are identical to the first embodiment of the latter, except for this which is the detection of the dust which is carried out by means of an error of the coded data contained in the signal HF, as it is the case when the recording of the information

  is carried out by the PCM method (pulse code modulation).

  In the case of the embodiment of FIG. 7, encoded data contained in the RF signal is provided to the coding error detection circuit 18 When an error of the coded data is detected by the coding error detection circuit 18 , signals, such as an error detection signal and an interpolation order signal, are generated and applied to a counting circuit 19 In the counting circuit 35 19 which is for example designed in the same way that the counting circuit 3, the number of appearances of the error detection signal or the interpolation order signal during the predetermined period of time is counted. When the count value has reached a predetermined number, a signal of high level output is generated and supplied to the timing circuit 4 as a dust detection signal. After this, the dust detection is signaled by the signaling device 5 in the same manner. st

  than in the previous embodiments.

  In the case of the embodiment of FIG. 8, the error detection signal or the interpolation command signal generated by the coding error detection circuit 18 is applied to an integrator 20.

  The integrator 20, for its part, generates a voltage signal whose level corresponds to the number of appearances of the coding error detection signal or the interpolation order signal. The output signal of the integrator 20 is then compared to a predetermined reference voltage in a comparator 21, and hence the comparator generates a dust detection signal when the number of coding error detection signals or interpolation order signals generated during a The dust detection signal from the comparator 21 is then supplied to the timing circuit 4 and the dust detection is signaled by the signaling device in the same manner as in the signaling modes.

previous realization.

  It follows from the foregoing that, by virtue of the present invention, the presence of dust on a recording medium, for example, can be detected and reported or indicated. Accordingly, stable operation of the reading system, such as a system for reading video and / or sound information, can be provided by cleaning the surface of the recording medium, a magnetic reading head or mirrors constituting the components of the reading system, as indicated by the signaling device Thus, it becomes possible to obtain a good image and / or a perfect sound from the reading system, and moreover a faulty operation of the servo-control of the reading system can

  be avoided so as to ensure the stability of the reading operation.

  It will be understood that the foregoing description has been given by way of illustration only and does not have the effect of limiting the scope of the invention.

  On the contrary, many embodiments equivalent to the preferred embodiments described above fall within the given definition.

by the appended claims.

  By way of example, it is possible to use a monostable multi-vibrator or a flip-flop light-emitting diode, a liquid-crystal element or an alarm equipped with a vibrator Finally, instead of a signaling of the presence of dust, it is possible to adopt a light-emitting diode. other solutions such as stopping or pausing the read operation

  or ejecting the recording medium.

  On the other hand, in the case of an information pickup device using an electrostatic type reading apparatus, the remaining life of the pickup can be indicated or displayed together with the detection of the presence of This is made possible by the fact that the wear of the reading tip causes a change in the frequency characteristics of the output signal of the reading apparatus, which results in a corresponding variation in the amplitudes. of the video information and sound information, and the remaining life of the reading tip can be estimated from the difference between the amplitudes of the

carrier waves.

Claims (11)

  1 Device for detecting and signaling the presence of dust or other foreign bodies in an information extraction system, characterized in that it comprises: a dust detection means (2, 3, 6 to 21) for detecting an abnormal state of an extraction signal taken from a recording medium and generating a dust detection signal; maintenance means (4) for maintaining said dust detection signal for a predetermined period of time and generating an output signal during said predetermined period of time after a last reception of said dust detection signal; and a signaling means (5) for signaling the presence of dust   according to the output signal of said maintenance means.   Detection and signaling device according to claim 1, characterized in that said dust detection means comprises a level loss detection means (2) for detecting the absence of said extraction signal and generating a signal of level loss detection, and means (3, 6) responsive to said level loss detection signal for generating said dust detection signal in accordance with a frequency of the level loss detection signal within a predetermined period of time.   3 detection and signaling device according to claim 2, characterized in that said means responsive to the level loss detection signal comprise a counter (3) for counting the level loss detection signal and generating the signal for detecting dust when said level loss detection signal is generated more than a predetermined number of times within a predetermined period of time.  4 A detection and signaling device according to claim 2, characterized in that said means responsive to the level loss detection signal comprise an integrator (6) for integrating said level-loss detection signal and a comparator ( 7) for comparing an integrator output signal with a predetermined reference threshold and for generating the dust detection signal when the   output signal of the integrator becomes greater than said reference threshold.   A detection and signaling device according to claim 1, characterized in that said dust detection means comprises an amplitude detection means (8, 11) for, in response to said extraction signal, generating a representative output signal of an extraction signal amplitude, and means (9, 10 and 12) for, in response to this output signal of the amplitude detection means, generating the dust detection signal in accordance with an instantaneous level. of the signal   output of said amplitude detection means.   Detection and signaling device according to claim 5, characterized in that said amplitude detection means comprises an envelope detector (8) for generating an envelope signal of said extraction signal, and said means responsive to the output signal of the amplitude detection means comprises a comparator (9) for comparing a level of said envelope signal with a predetermined reference threshold and generating an output signal when the envelope signal level becomes higher reference threshold, as well as a bandwidth detector (10) for generating the dust detection signal when the comparator output signal is generated beyond a predetermined period of time.   Detection and signaling device according to claim 1, characterized in that said amplitude detection means comprise level detection means (11) for detecting a level of said extraction signal and said means responsive to the output signal of the sensors. amplitude detection means comprises a comparator (12) for comparing an output signal of said level detecting means with a predetermined reference threshold and for generating the dust detection signal when the output signal of said detecting means of   level becomes greater than the reference threshold.   Detection and signaling device according to claim 1, characterized in that said dust detection means comprise level detection means (13, 16) for detecting a variation in the level of an error signal component representing an error of an extraction position and contained in the extraction signal and for generating an output signal representative of said level variation, and means (14, 15 and 17) responsive to said output signal of the detection means level for generating the dust detection signal according to the generation of the output signal of the level detection means.  A detection and signaling device according to claim 8, characterized in that said level detecting means comprises an envelope detector (13) for generating an envelope signal of a focusing signal component contained in said extraction signal and said means responsive to the output signal of the level detection means comprise a comparator (14) for comparing said envelope signal with a predetermined reference threshold and for generating an output signal when the signal level envelope becomes greater than the threshold   reference, and a pulse width detector (15) for generating the dust detection signal when the comparator output signal is generated beyond a predetermined period of time.   A detection and signaling device according to claim 8, characterized in that said level detecting means comprises a comparator (16) for comparing a level of a focus error signal component and a level of a track error signal component contained in the extraction signal and generating an output signal when the difference between the levels of the error signals becomes greater than a predetermined value, and said means responsive to the output signal of the means. level detecting means comprises a counter (17) for counting the comparator output signal and generating the dust detection signal when the comparator output signal is generated more than a predetermined number of times within the comparator; 'a period predetermined time.   Detection and signaling device according to claim 1, characterized in that said dust detection means comprises error detection means (18) for detecting an error in the coded data contained in said extraction signal and generating an error detection signal in response to detecting said error, and means (19, and 21) responsive to said error detection signal for outputting the dust detection signal in accordance with a frequency of generating said signal error detection within a period of predetermined time.   12 detection and signaling device according to claim 11, characterized in that said means responsive to the error detection signal are constituted by a counter (19) for counting said error detection signal and generating the signal of dust detection   when the error detection signal is generated more than a predetermined number of times within a predetermined period of time.   13 A detection and signaling device according to claim 11, characterized in that said means responsive to the error detection signal comprises an integrator (20) for integrating this error detection signal and generating an integration signal and a comparator (21) for comparing said integration signal with a reference signal and for generating the dust detection signal when the level of said integration signal becomes higher than that of the reference signal.