JPS60246026A - Servo errors reducer for optical reproducer - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a disc playback device, and more particularly, to a disc playback device, and more particularly, to focusing a light beam on the surface of a disc and detecting selections on the disc surface with the focused light beam. The present invention relates to an apparatus useful in systems for reducing errors caused, for example, by disk eccentricity, in tracking recorded data tracks.

PRIOR ART High density optical recording devices that can be used to record and reproduce information are known in the prior art. For example, 1
On June 27, 978, “°Multilayer Optical Record (MU)
lti-Layer 0ptical Record)
” U.S. Patent No. 409'7859
The invention described in the specification relates to an optical disc recording/reproducing device in which data is recorded on the surface of a recording medium. In the device of the above-identified US patent, the thermal energy of a focused, high-intensity light beam causes changes in optical properties on the surface of a recording medium. For example, in some equipment,
Due to the thermal effect of the laser beam, approximately 1011
The bit information is recorded.

In an optical playback device, a disc record is rotated on a turntable while a light beam scans the surface of the record with information recorded on the surface. Optical devices direct a beam of light onto an information-bearing surface (when using the device described in the above-mentioned U.S. patent,
In order to read out the densely recorded information on the disk surface, the light beam must be guided precisely to the center of the track of recorded pits, and the light spot must cover only a very small area. It is necessary to focus the light onto the surface of the disc record. In the best configurations, the light spot size is diffraction limited.

Problems associated with the physically limited dimensions of the disc and playback equipment make it difficult to keep the light spot guided on the track of the pits and to keep the light spot focused on the surface of the disc. is difficult to maintain.

If the mounting hole of the disk is not precisely centered with respect to the data track, the recorded data track will be eccentric due to mechanical positioning of the disk after removal and reinstallation of the disk. Surface errors caused by distortions and deformations of the surface structure, in particular deformations due to temperature effects, give rise to eccentricity problems of pre-recorded tracks which distort the form of the track position. The third cause of eccentricity in the track is due to the swinging of the shaft of the turntable in its supporting bearing.

It is known to use a servo loop in a tracking device to compensate for eccentric movement of a data track with respect to a fixed tracking beam. Eccentric motion tends to repeat on adjacent tracks with each rotation of the disk. It is known to predict errors at several positions on a disk and to provide appropriate complementary fi'V Ill signals to the servo system. According to this, the bandwidth required for the servo device can be reduced. February 6, 1979 Disc Eccentricity Compensator (Disc E)
ccentricity compensating S
U.S. Patent No. 41 entitled “system)”
No. 38,741, the reference track is read,
A device is shown in which a "symbol" waveform corresponding to the tracking error signal is generated and stored. This waveform is then provided to electronic circuitry that controls the disk tracking device during a subsequent read operation. .1982
dated December 21, 2013
In U.S. Pat. A scheme is shown in which the computation is done by an open-loop control circuit that counts the number of crossings of the detected signal track.

The device described in the above-referenced U.S. Pat. Adequate tracking error compensation can be provided for 2 disks, but is insufficient for plastic disks. They tend to be on plastic substrates. Therefore, plastic
In the case of disks, a tracking compensation signal based on a reference track at a first radial distance would be completely inadequate for tracks at different radial distances, as disclosed in the above-mentioned US Pat. No. 4,138'741. The device described in the report would be more harmful than effective. In the case of plastic disks, a compensating tracking signal based on a signal reference track is insufficient.

In addition to the problems with keeping track of recorded data, there are problems with maintaining focus on the surface of the disc. This focus problem is caused by imperfections in the disk, turntable, or rotational drive mechanism that can shift the information-bearing surface of the rotating disk relative to a fixed point. As with tracking problems, disk surface irregularities can be due to non-uniform manufacturing thicknesses as well as deformations imposed by thermal and rotational stresses.

The servo device for controlling the distance between the objective lens and the rotating disk was introduced on November 29, 1983 as “Lens Position Control Device for Optical Reproducing Devices (LensPosi)”.
tioning (Eontroller for 0
ptical Playback Apparatus
)” U.S. Patent No. 4,418,405
This is shown in the specification of the No. However, the device shown in this patent does include a device for predicting errors, even in the case of tracking errors, where focusing errors occur on adjacent tracks on each revolution of the disk. There is a tendency to repeat.

<Summary of the Invention> The present invention is implemented in an apparatus for reproducing information recorded on the surface of a rotating disk medium.

In this apparatus, each of one or more parameters associated with the medium is pushed from a sensed state toward a desired state during successive rotations of the medium. To this end, servomechanism means are provided, the servomechanism means being responsive to the state of the parameter for generating each successive error signal representative of the deviation of the state of the parameter from the desired state. and (to) an error signal and a position signal representing the angular rotational position of the rotating recording medium.
(0) control means for varying the state of the parameter toward its respective desired state in response to the control signals;

According to the invention, the position signal consists of a train of pulses generated during each rotation of the medium, with each pulse in each train marking the passage of the medium through each angular position of the medium. The measuring means includes encoding means for encoding each successive error signal into each error data word in response to the occurrence of a pulse in each pulse train, and one
or more data storage means. Each data storage means has a position corresponding to each angular position of the medium and a position corresponding to each pulse in each pulse train from the position signal. Each location in each data storage means then stores a respective historical data word.

The measuring means further comprises calculating means, the calculating means being operable on each pulse occurrence in each pulse train to combine each error data word with a historical data word retrieved from each position of each data storage means. Generate control data words. The measuring means further operates on the occurrence of each pulse in each pulse train to convert each control data word into a respective one of successive control signals.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The structure, features, and effects of the present invention will be described in detail below according to preferred embodiments shown in the accompanying drawings.

DESCRIPTION OF THE EMBODIMENTS Reference is made to FIG. 1, which shows an optical disc playback device. A record disc 10, placed on a turntable lo and held in place by a pressing device 14, is rotated by a drive motor 16.

The clamping device 14 is shown only functionally. In fact, the disk 10 may be positioned by a vacuum chuck instead of by pressing. An encoder 18, shown as an angular incremental encoder mounted on the shaft 17 of the drive sweater 16, generates electrical pulses corresponding to the position of the shaft 17 and provides position information regarding the disk 10. The two signal outputs of encoder 18 are coupled to processing controller 56 . The first signal output is an index pulse signal generated once per revolution, and the second signal output is an angular segment pulse signal. For example, 1024 equally spaced pulses or segments are generated per revolution.

Disc 10 is a photosensitive information record dated September 9, 1980.
It may be of the type described in U.S. Pat. Disk 10 has at least one surface 2
It has information recorded in 0. According to one recording technique for recording information by removing material, the material of the recording layer is raised to a removal temperature. During the recording process, the material of the recording layer is evaporated or dissolved to form pits therein. By appropriately modulating the intensity of the light beam according to the recording signal, the path of the light beam can be adjusted to
Material is removed in successive areas of the record, the removed parts forming information tracks consisting of pits in areas separated by undisturbed areas of the recording layer (areas not exposed to the intense light beam). Ru.

The data recorded on the surface 20 of the disc]O is read by the optical disc playback device shown in FIG. The monochromatic light output of laser 22 is directed through polarizer 24 to polarizing beam splitter 26 . Polarizer 24 deflects the laser output in a direction that allows the light to pass through beam splitter 26 . Lens 28 directs the light that has passed through beam splitter 26 through a quarter-wavelength (λ/4) plate 30 and onto a galvanometer-controlled mirror 34 that reflects the beam in a direction that passes through objective lens 33. the beam is focused onto the information-bearing surface 20 of the rotating disk 10. As mentioned above, in the read mode of operation, the output intensity of the laser 22 is set at a safe constant level below the level at which absorbing layer material is removed.

The reflected light from the information surface 20 is transmitted through elements 33, 34, 30128.
and then returned to the beam splitter 26. Since the returned light has passed through the λ/4 plate and the three metal plates zero times, its polarization is determined by the beam splitter 26, which converts the change in optical energy into an electrical signal, shown as a photodetector 38 in FIG. The direction is changed to reflect the light beam back.

To optically scan the surface 20 of the rotating disk 10, the conversion stage 36 is moved radially across the disk 1o at a speed as required by the desired playback mode. The conversion stage 36 includes each element of the optical device, namely the beam splitter 26, the lens 28, the λ/4 plate 301, the galvanometer 32 and its mirror 34, the objective lens 4 and its positioning drive. The device 31 and the photodetector 38 are moved. Signals from a converter stage drive (not shown) cause the converter stage 36 to be moved such that the light beam passing through the lens 3:5 is within several tracks of the desired location on the surface 20 of the disk 10. i.e. coarse tracking movement).

Fine tracking movement is performed using a normal galvanometer controlled mirror 34.
This is done by guiding a light beam precisely to the desired track. The galvanometer 32 rotates a mirror 34 about an axis parallel to the reflective surface 2o of the disk 10, so that the light spot formed by the lens 33 is aligned with the disk 10.
be guided along the selected track as it rotates. Mirror 34 is energized by galvanometer 32 in response to a control signal provided by galvanometer driver 52 .

Light beam 35 is focused onto surface 20 of disk 10 by focusing objective 33 . Lens potentiometer 31 moves lens 33 back and forth in the direction indicated by the arrows to maintain proper focus. Lens potentiometer 31 is responsive to a focus drive signal generated by drive 54. This may be of the type shown in the aforementioned US Pat. No. 4,418,405.

The intensity of the light falling on the photodetector 38 alternates between a minimum and a maximum level as successive pits and undisturbed areas of the information surface 2o pass through the path of the focused beam. The light reaching the photodetector 38 will be at a minimum intensity level when the undisturbed areas in the absorption layer of the disk 10 are in the focused beam path, while the pits are in the focused beam path. At this time, the light reaching the third photodetector is at its maximum intensity level.

The output of photodetector 38 consists of a pulse-encoded modulated wave that varies according to the pit edge spacing. The detected beam intensity changes are representative of the original signal encoded on the surface 20 of the disk during the recording operation. The data signal provided by photodetector 38 is connected to regeneration electronics (not shown).
and process the information content. This data signal is also provided to a lumped error signal generator 40 and a tracking error signal generator 42.

The tracking error signal passes through a filter 44 that attenuates high frequency noise that is unrelated to the angular position of the disk.

The filtered tracking error signal is provided to amplifier 46 which adjusts the signal level for processing by error reduction circuit 60. Circuit 60 operates on the tracking error signal as shown in more detail in FIGS. 2 and 3;
This provides a signal to the galvanometer driver 52, which in turn provides a drive signal to the galvanometer 32.

The focus error signal is passed through a filter 48 similar to filter 44 to attenuate high frequency noise independent of the angular position of the disk. The filtered focusing error signal is provided to amplifier 50 and the signal level is adjusted for processing by error reduction circuit 60. Circuit 60 operates on the focus error signal in the manner described in detail in connection with FIGS. 2 and 3, thereby providing a signal to focus drive 54. Focusing drive device 54 provides a drive signal to focusing lens positioning device 31 .

Next, a second diagram illustrating the error reduction circuit 60 of FIG. 1 in further detail.
See diagram. Elements of FIG. 2 that are shown in FIG. 1 have the same reference numerals. In this figure, the error reduction circuit 60 includes switches 62, 72, an analog-to-digital converter (A/D) 64, an arithmetic logic unit (ALU) 68, a memory storage device 70, 72, a data bus 66, and a digital-to-analog converter. Instrument CD/A) 7
4, and sample-and-hold circuits 80, 82.

The two error signals provided by amplifiers 46 and 50 are provided to the input terminals of switch 62.
selectively directs one of the input signals to an output terminal by a signal provided to a control input terminal (C) of switch 62 under control of processing controller 56 . The selected switch input 4g is supplied to an A/1) converter 64, which converts the input analog signal into a plurality (for example, eight) of two signals and supplies them to a data bus 66. . Timing and sample-and-hold functions generally associated with A/D conversion functions are also provided, but not explicitly shown.

The digital data represented by the binary output signal of the φ converter 64 is associated with a first memory device (T memory) 70 for tracking errors and a second memory device (F memory) for lumped errors. ALU in connection with 72
68. After the operation of ALU 68 is completed, as shown in more detail in FIG. converted to an analog signal.

This signal is supplied to the sample-and-hold circuits 8o and 8 by the switch 76 under the control of a signal supplied from the processing controller 56 to the control input terminals (C) of the switch 76.
2, and is supplied from these sample-and-hold circuits 80 to the galvanometer drive device 52 or the focusing drive device 54.

In the example of the invention, encoder 18 provides 100 Hz per rotation of disk 10 to process process controller 56 .
24 pulses are generated, each of the off-tracking memory 70 and the focusing memory 72 having the width of the data bus 66;
In this example, 1 for data words with width equal to 8 bits.
It consists of 024 memory locations.

Processing controller 56 responds to pulse signals from encoder 18 to control tracking memory 70 and focusing memory 7.
Generates an address signal to 2. Therefore, each memo 1J7
Each data word in 0.72 corresponds to an angular position on disk 10 with respect to a fixed index pulse determined by the index pulse. The contents of each of these memory words are recorded in Tracking Memo 1J7.
0, it is reflected by the galvanometer control mirror 34;
A drive signal of the direction and magnitude necessary to maintain beam 35 directed onto the desired data track of disk 10 and, in the case of focusing memory 72, position lens 33 properly relative to surface 20 of disk 10. drive signals of the direction and magnitude necessary to maintain alignment at the correct focal position.

In accordance with the principles of the invention, in this example 10 of the disks 10 are designated by signal pulses from the encoder 18.
During each period corresponding to one of the 24 angular segments, A
The LU 68 receives a data word consisting of a digital signal corresponding to a tracking error and stores the received data word in a tracking memory 70 corresponding to a particular angular position of the disk 10, in accordance with the human power properly directed by the switch 62. , the combined data word is stored back in the same location in memory, and the combined data word is provided to a D/A converter 74 where the data is The signal is introduced into a sample-and-hold circuit 80 via the appropriate output terminal of switch 76. Sample-and-hold circuit 80 samples the tracking signal at an appropriate time due to φT and transmits it to tracking galvanometer driver 52. During the same period, switches 62 and 76 are energized to direct the focused error signal and incorporate the focused drive 54 into a loop with the error reduction circuit 60. The same process uses the accumulated data in the focused memory 72. This is repeated, and at an appropriate time determined by φF, the focusing signal is clocked into the sample-and-hold circuit 82, and a driving signal is generated from the focusing driver 54.The processing for handling this dual function error signal is Iterates continuously for each angular position during each of the ten rotations.

FIG. 3 shows a detailed flow diagram of the above process, including the initial state of the contents of storage locations in memories 70 and 72. The steps in Figure 3 are for ALU 68 and memo 17.
Processing controller 56, which typically can be a microprocessor, via control signals provided to 70 and 72
executed within. This error handling process represents a very small portion of the processing power of a typical microprocessor and can be conveniently integrated into the functionality of the optical disk drive's main controller.

The procedure begins at step 101, where both the tracking memory 70 and the focusing memory 72 are stored in this example at 102.
All four storage positions are cleared or set to O. Then, in step 102, the processing device
It is in an idling state waiting for a pulse from the encoder 18 indicating the index mark. disc 1
The corresponding location on 0 is referred to as location 0 and is associated with storage location 0 in memories 70 and 72. Thus, in step 103, memory indication register X is set to O.

Steps 104-108 include processing for handling tracking errors. At step 104, the digitized data word representing the tracking error, ie, the difference between the expected galvanometer position and its actual position, is read onto data bus 66 and directed to ALU 68. Step 1
At 05, this data word is combined with the contents of storage location X of tracking memory 70 to produce a data word referred to as T SUM. (Initially, the first
During the rotation period of , the contents of the storage location X of the memory 70 are 0).

The process of step 106 inquires whether the mode of the device requires updating the contents of tracking memory 70. During the initial rotation period of the disk 10, the answer is always YES in order to set the initial value in the memory 70.
”.Furthermore, during the data recovery operation, the memo IJ
Maintaining '/Q continuously and dynamically updated is extremely effective and, in fact, is a major feature of this invention]
It is one. Therefore, step ], O'7 is almost always entered (entered "-") and the updated error data word TSUM is stored in location X in the tracking memory 70. TSUM is then This is applied to transducer 74 which generates the appropriate galvanometer drive signal which is generated by drive 52. This completes the tracking error processing for the Xth position.

Steps 109-113 correspond exactly to steps 104-108, except that they deal with focusing errors.

These steps 109-113 are performed after switches 62 and 76 are placed in position to read the focus error signal and generate the focus drive signal.

Step 114 waits for the next timing pulse from encoder 18. When this is received, the value of X is incremented in step 115, and if X is not equal to 1024, the tracking error handling procedure for the next position on disk 10 is entered in step 104. When X is increased to 1024, indicating that an index mark is present, the X register is set to step 10.
3 to O to ensure tracking error handling procedures.

Accordingly, error reduction circuit 60 provides drive signals to tracking drive 52 and focusing drive 54 in response to the error signals generated by error signal generators 40 and 42. Tracking memory 70 and focusing memory 72 may store expected error values of tracking and focusing positions for multiple positions around disk 10 . Finally, ALU 68 and memory 70.
The process of FIG. 3 carried out by controller 56 providing appropriate instructions to 72 causes the accumulated error values to be dynamically updated 7 on each revolution of disk 10, thereby causing generators 40 and 42 to Ensure that the generated error signal is minimized.

The filters 44 and 48 have been described as having low-pass characteristics. Additionally, using the constant period error update procedure described above, filter 44 may be selected to minimize the rms tracking error in the presence of noise generated by photodetector 38. In this sense,
The error reduction device of the present invention has a tracking error (
Kalman) filter. Similarly, filter 48 may be selected to minimize the rms concentration error in the presence of photodetector noise. Therefore, the error reduction device can also be implemented by a Kalman filter with respect to the focusing error.

Although the principle of the present invention has been explained above with reference to the embodiment shown in the drawings, the present invention can also be practiced with various configurations different from those of the above-described embodiments to obtain the desired effect. can. It goes without saying that this invention number is included in the invention number 5.

[Brief explanation of drawings]

Fig. 1 is a block diagram of an embodiment of an optical reproducing device embodying the present invention, Fig. 2 is a detailed plan view of the error reduction device shown in Fig. 1, and Fig. 3 is a block diagram of an embodiment of the error reduction device shown in Fig. 2. Figure 3 shows a flow chart showing the steps performed by the device. 10...Disk medium, 2o...Surface, 68...
Calculation means (ALU), patent applicant: RCSNY Corporation agent' Tetsu Shimizu (2 persons)

Claims (1)

[Claims] (1) In a device for reproducing information recorded on the surface of a rotating disk-shaped medium, a device related to the medium
Each of the or more parameters is pushed from a sensed state towards a desired state during successive rotations of the medium, and to do this, (a) responsive to the state of the parameter; (1)) sensing means for generating successive error signals each representing a deviation of a state of a parameter from a desired state; a servomechanism comprising measurement means for generating respective successive control signals for each parameter; and (0) control means for changing the state of the parameter toward its respective desired state in response to said control signal. Means are provided, said position signal comprising a train of pulses generated during each rotation of said medium, each pulse in each pulse train marking passage of said medium through each angular position of said medium, and said measuring The means includes encoder means for encoding the level of each successive error signal into each error data word in response to the occurrence of position signal pulses in each pulse train, and one or more data stores, each corresponding to each parameter. means, each data storage means having a position corresponding to each angular position of said medium and each pulse in each pulse train from said position signal, and each position in each data storage means having a position corresponding to each pulse in each pulse train from said position signal; and operating on the occurrence of each pulse in each pulse train to combine each error data word with a historical data word retrieved from each position of each data storage means to produce a control data word. Servo error for an optical reproduction device, comprising calculation means and decoder means operative on the occurrence of each pulse in each pulse train to convert each control data word into a respective one of said successive control signals. Reduction device.