U.S. Philips Corporation

Antonius H Akkermans

Gijsbertus Bouwhuis

Albert Smid

Robertus W Groen

Jozef P Benschop

Guido C Van De Looy

Henri Cloetens

Johannes L Van Velthoven

Cornelis J Rooyackers

Theodorus A Koopmanschap

Anthonius L Dekker

An optical beam in a scanning device is focused on an information layer of a multi-layer optical record carrier. A focus control circuit keeps the focal point of the beam on the information layer. When the focal point jumps to another information layer, the focus control circuit does not monitor the so-called central aperture signal in order not to depend on the presence of information in the information layers. During the jump the characteristics of the feedback loop of the focus control unit are modified to avoid instabilities in the movement of the focal point during the jump. The characteristics of the feedback loop are restored after a predetermined period of time, then the focal point is near the designated layer and the restored control loop focuses the focal point on the designated layer.

Optical scanning apparatus for a multi-layer record carrier, including a

An optical beam in a scanning device is focused on an information layer of a multi-layer optical record carrier. A focus control circuit keeps the focal point of the beam on the information layer. When the focal point jumps to another information layer, the focus control circuit does not monitor the so-called central aperture signal in order not to depend on the presence of information in the information layers. During the jump the characteristics of the feedback loop of the focus control unit are modified to avoid instabilities in the movement of the focal point during the jump. When the focal point is captured on the designated information layer, the characteristics of the feedback loop are restored.

A scanning device includes a transducer which scans the tracks of a record carrier by a scanning point of radiation. The transducer is mounted movably on a slide which can be displaced in a direction transverse to the tracks by means of a slide drive motor. At least a portion of the transducer is movable relative to the slide, by energizing an actuator. A tracking Control circuit keeps the scanning point on a track by adjusting the actuator control signal (Va) as a function of a tracking error signal. A slide speed control circuit controls the speed of the slide according to a predetermined speed profile provided by a slide speed reference signal (Vrefs). A scanning point speed control circuit controls the speed with which the scanning point is displaced transverse to the tracks so it is maintained substantially equal to the slide speed. The device may be used in a tracking mode and in a displacing mode. In the displacing mode the tracking control circuit is active. In the tracking mode the slide speed control circuit as well as the scanning point speed control circuit are active.

Scanning device with two-stage controller for positioning a scanning

Scanning apparatus for a disc-shaped record carrier having a spiral track, the apparatus including a scanning head arranged on a slide which is radially displaceable with respect to the record carrier. The scanning point produced by the scanning head is maintained on the track by a tracking control system which includes a fine positioning device secured to the slide and which radially displaces the scanning point within a predetermined limited range of displacement determined by the positioning of the fine-positioning device with respect to the slide. A position-indication signal (PS) indicative of such position is generated, and a control unit detects when such signal exceeds a predetermined limit value. In that event, the control unit energizes a driving motor of the radial displacement device by supplying an energizing pulse pattern thereto which causes displacement of the slide to a position at which the position-indication signal returns to a value below the limit value. The energizing pulse pattern is adjusted by the control unit so that the displacement of the fine-positioning device in response thereto remains within predetermined limits and/or is symmetrical about a central position of such device relative to the slide.

Record carrier scanning apparatus wherein the scanning head is

A device for scanning a record carrier having essentially parallel tracks produces detection signals (AS, . . . , FS) which depend on the location of the scanning point relative to the tracks and from which are derived a tracking error signal (RE) and a track position signal (TP). A comparator (7) detects whether the track position signal intersects a first threshold (D1), and a comparator (6) detects whether the tracking error signal is located within an amplitude window established by a second positive threshold (D2) and a third negative threshold (D3). A signal processor (8) derives a track loss signal from the results of the detections performed by the comparators (6, 7), which track loss signal signifies that the scanning point no longer follows the track. The track loss signal is not produced unless an intersection of the first threshold by the track position signal is detected and, furthermore, the tracking error signal is outside of the amplitude window during a specific time window around such intersection. In this way, momentary disturbances of the detection signals caused by narrow interruptions of the tracks, due to record carrier errors, do not result in erroneous track loss signals.

Device for scanning a record carrier

Scanning apparatus for an optical record carrier includes a position control loop, a focus control loop, and an adjustment circuit for stabilizing a control parameter of each loop such as the gain and frequency transfer characteristic thereof. To detect the value of the control parameter of a control loop a calibration signal of relatively high frequency is intermittently introduced therein. This makes possible more sensitive detection of the loop response than if a low frequency calibration signal were employed. Despite the higher frequency, the power consumption of the apparatus due to the calibration operation is relatively low because the calibration signal is only intermittent. The adjustment circuit detects the signal produced by a control loop in response to the calibration signal and by comparison therewith derives an adjustment signal for adjusting the control parameter of such loop. The adjustment signal is stored in digital form, whereby it is retained without drift even during off intervals of the calibration signal. Switching means are provided for enabling the loop adjustment circuit to be selectively connected to either control loop. Such switching means may take the form of a programmable digital control unit.

Method and means for detecting and stablizing control loop parameters of

A read and/or write device for a record carrier having tracks which extend substantially parallel to each other. A read and/or write head for scanning the tracks is moved by a positioning system in a direction transverse to the tracks. During such movement a counter derives the number of tracks traversed per unit time from the number of reference level crossings of a periodic signal V.sub.sp having a frequency corresponding to the track crossing frequency. Counting of spurious level crossings is inhibited by blocking the counter during a blocking interval (tbl) following each level crossing which is counted. The speed of the read and/or write head is controlled on the basis of the counted level crossings.

Read and/or write device

A beam splitter (120) arranged in the radiation path of the scanning beam splits off a reference beam synchronously moving with the scanning spot (21) to a reference plane (140). The movement of the scanning spot (21) can be checked by measuring, with the aid of a radiation detector (160), the movement of a reference spot (121) formed by the reference beam in the reference plane. In this way an accurate determination of the position of the scanning spot (21) is possible while using simple beam-deflecting elements (40,42) having a relatively low accuracy. A cylindrical lens (131) gives the scanning spot the shape of a line, so that sensitivity to dust and other contaminations on the reference plane is reduced considerably.

Scanning optical microscope with position detection grating

A device is described for detecting a magnification error in an optical imaging system comprising a lens system (L.sub.1, L.sub.2) which is telecentric at one side. Two gratings (RG.sub.1, RG.sub.2) arranged in the object plane (MA) are imaged onto two gratings (WG.sub.1, WG.sub.2) arranged in the image plane (W; WT) and the radiation beams (b.sub.1, b.sub.2) by means of which these images are formed are incident on two radiation-sensitive detection systems (D.sub.1, D.sub.2) which supply periodic signals (S.sub.1, S.sub.2). By phase comparison of these signals a magnification error (S.sub.ME) and, if desired, a focussing error can be measured very accurately.

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Eindhoven, Netherlands

Antonius H Akkermans