KR20000005156A - Closed loop servo operation for focus control - Google Patents

Abstract

PURPOSE: A closed loop servo operation technique is disclosed for focus control of a beam of radiant energy. CONSTITUTION: A detector (712) of the beam has first (368) and second (376) outputs responsive to a position of the focal point of the beam. A circuit is coupled to the outputs of the detector for producing an error signal representing a displacement of the focus from a predetermined position, wherein the error signal has a periodic characteristic relative to the displacement. A servo (700) responsive to the error signal restores the displaced beam to the predetermined position. A local feedback loop (344) is coupled to the outputs of the detector, and includes first (360) and second (364) periodic function generators, each responsive to the error signal. The second periodic function generator has an output that differs from an output of the first periodic function generator by a phase angle, preferably 90 degrees. A first multiplier (332) multiplies the first output of the detector by the output of the first periodic function generator. A second multiplier (336) multiplies the second output of the detector by the output of the second periodic function generator, wherein the outputs (460, 472) of the first and second multipliers are provided as inputs (476, 480) of the circuit to modify the error signal.

Description

Closed-loop servo motion for focus control

In an optical disc drive in which information is stored in a plurality of spiral or concentric information tracks, the lock of the recording or reproduction beam on the information track of interest is typically held by a tracking servo, for example For example, such a surge is disclosed in US Patent Publication No. 4,332,022 by Ceshkovsky et al. Tracking servos react to minimize the error signal Vp resulting from the intensity of the light beam reflected back from the optical disc medium, which is given by the following equation:

here,

A is a constant;

x is the displacement of the beam from the track center; And

p is the track pitch.

Terashi, in US Pat. No. 5,177,725, discloses a servo device that extends a pull-in range using a speed detector that detects the speed of a drive element.

Kobayashi et al., In US Pat. No. 4,853,918, show that signals from the tracking of pits offset each other around a track center are provided to the sample-and-hold circuit, and compared with each other to have teeth with discontinuities in the middle between the tracks. A device for obtaining a tracking signal is proposed.

US Patent Publication No. 4,779,251 to Burroughs discloses an apparatus that includes a ramp waveform generation circuit used to introduce a controlled offset to a tracking servo. The servo error signal, resulting from the pre-formatted precision tracking features, is inverted in phase when the readout beam moves between the tracks. The inclined waveform is adjusted in accordance with the tracking error information stored from previous microjumps between the tracks.

In applications related to focus control, the focus servo operates in the negative feedback area of the focus error "S curve". Typically, using open loop operation, a special sequence is required to place the servo in the negative region surrounded by the positive feedback regions. If for some reason the focus is lost, the entire capture sequence must be repeated. This is very time consuming.

Summary of the Invention

It is a primary object of the present invention to extend the operating area of a focus servo operating in closed loop mode.

It is another object of the present invention to improve the function of the focus servo and to automatically refocus the focus in response to disk defects, noise, shock and vibration.

These and other objects of the present invention are achieved by providing an optical pickup having a plurality of outputs for generating an error signal that feeds a servo loop in an optical disk drive. This error signal is also supplied to the local feedback loop, which feeds the output of the optical pickup so that the focus error signal plotted against the position of the read beam is converted from a sinusoidal waveform to a substantially linear gradient. It includes a plurality of sine function generators to change. The local feedback loop can be designed to share elements such as the main tracking servo loop, but is separate from the main tracking servo loop.

In addition to the sine function generators, the local feedback loop includes two multipliers, a difference summator, a local loop gain element, a phase compensator, and a summation circuit that adds a phase shift value to one of the two input stages of the sine function generator.

The present invention provides an apparatus for controlling a beam of focused radiant energy, which device acts on the optical element to orient the focused beam, focusing the focused beam in a predetermined position direction. An actuator, and a detector for receiving light from the beam. This detector responds to the displacement of the focal point of the beam from a predetermined position. Circuitry connected to the output ends of the detector generates an error signal indicative of the displacement of the focal point of the beam from a predetermined position. The servo is connected to an actuator and an error signal, which in response to the servo shifts the focus of the beam to a predetermined position.

According to the invention, a local feedback loop circuit is connected to the output terminals of the detector. The loop includes a first periodic function generator responsive to an error signal and a second periodic function generator responsive to an error signal. The second periodic function generator has an output that is different in phase angle from the output of the first periodic function generator. The loop includes a first multiplier that multiplies the detector's first output with the output of the first periodic function generator and a second multiplier that multiplies the detector's second output with the output of the second periodic function generator, the first and second multipliers. Outputs are provided as inputs to this local feedback loop circuit.

According to a feature of the invention, the periodic characteristic is substantially sinusoidal and the first periodic function generator and the second periodic function generator are sine generators.

According to another feature of the invention, the first and second outputs of the detector have an approximately mutual quadrature relationship with respect to the displacement of the beam, and the phase angles are approximately 90 degrees apart. This phase angle can vary from about 60 to 120 degrees.

The present invention provides a method of focusing a beam of radiant energy, the method comprising generating first and second detection signals in response to a focus position of the beam, and receiving an error signal indicative of displacement of the focus from the predetermined position. Performed by the generating step, the error signal being periodic with respect to the displacement. The method includes generating a first periodic signal in response to an error signal, and generating a second periodic signal in response to the error signal, thereby returning a focal point separated by the displacement to a predetermined position in response to the error signal. The second periodic signal is different in phase angle from the first periodic signal. The error signal is obtained by multiplying the first detection signal and the first periodic function to produce a first multiplication signal, multiplying the second detection signal and the second periodic signal to calculate a second multiplication signal, And determining the difference between the second product signals. Preferably, the first and second detection signals and the first and second periodic signals are substantially sinusoidal.

To better understand these and other objects of the present invention, reference is made to the detailed description of the invention, which is read in conjunction with the following drawings, by way of illustration.

The present invention relates to a control device for an optical disk drive. More specifically, the present invention relates to improved servo control which extends the operating range of a closed servo mode of a focus servo or tracking servo to a plurality of points on a disc.

1 is a schematic diagram of an apparatus according to the invention.

2 is a partial view of the surface of a track-type optical recording medium.

3 is a block diagram of a signal recovery subsystem within the apparatus of FIG.

4 shows the subsystem shown in FIG. 3 in more detail;

5 is a spatial plot of a signal waveform corresponding to tracks on an optical medium.

6 is a schematic diagram of an electrical circuit of a portion of the device shown in FIG. 1;

7 is a block diagram of a sine function generator.

8 and 9 are electrical waveforms to help understand the present invention.

10 and 11 are schematic diagrams illustrating a particular embodiment of the present invention.

12 shows a ring detector used in the embodiment of FIGS. 10 and 11.

13 is a schematic diagram of an electrical circuit according to a preferred embodiment of the present invention.

14 is a detailed electrical circuit schematic showing the function generator shown in the schematic diagram of FIG.

FIG. 15 is a schematic diagram of a detailed electrical circuit showing a timing circuit of the circuit shown in FIG. 13; FIG.

16-18 are waveforms generated by the embodiment of FIG. 13.

19 is a schematic diagram of an electrical circuit of an alternative embodiment of the present invention.

20 is a comparison of operating characteristics of the embodiment of FIG. 19 with a conventional focus control system.

An optical system 10 of a disc player for information media such as video discs, magneto-optical discs, audio discs, computer data discs, collectively referred to herein as “optical discs” is shown in FIG. 1. The optical system 10 comprises a laser 18 adapted to generate a readout beam used to read an encoded signal stored on an optical disc 26, a first lens 28, Diffraction grating 30, beam splitting prism 34, and quarter wave plate 38. The optical system 10 further includes an objective lens 54 having a mirror 42 and an entrance aperture 58. The beam reaching the optical disc 26 can be moved in the radial direction by a known beam shifting device, indicated by inductor 52. Indeed, inductor 52 is controlled by tracking servo 94.

A portion of the enlarged optical disc 26 is shown in FIG. The optical disc 26 includes a plurality of information tracks 66 formed on the information bearing surface 70. Each information track 66 includes a continuum of light reflecting areas 74 and light non-reflecting areas 78. Light reflecting area 74 has a generally planar and highly polished surface, such as a thin layer of aluminum. The light non-reflective region 78 is generally a light scattering surface and appears as a raised or slightly raised portion on the plane representing the light reflecting region 74. The read beam 22 moves in one or more steps with respect to the surface 70 with the information of the optical disc 26, one of which is the radial movement indicated by the double arrow 82.

The readout beam 22 generated by the laser 18 first passes through the first lens 28, where the readout beam 22 is sufficient to fill the entrance aperture 58 of the objective lens 54. Used to make the fill size. Read beam 22 is shaped appropriately by first lens 28 and then passes through diffraction grating 30, which splits read beam into three separate beams (not shown). do. Two of these beams are used to generate a radial tracking error signal and the other is used to generate a focus error signal and an information signal. These three beams are equally processed by the rest of the optical system 10. As such, they are collectively referred to as read beams 22. The output of the diffraction grating 30 is applied to the beam splitting prism 34. The axis of the prism 34 slightly deviates from the path of the readout beam 22, as explained in more detail in US Patent No. 32,709, issued July 5, 1988, which is incorporated herein in its entirety. do.

The transmissive portion of the read beam 22 is applied to a quarter wave plate 38 which rotates the polarization of light forming the read beam 22 by 45 degrees. The read beam 22 then strikes the mirror 42 which redirects the read beam 22 towards the objective lens 54.

The function of the servo subsystem 94 is to track the indication of storing information on the surface 70 of the optical disc 26 in a radial direction so that the point of impact of the read beam 22 is defined by the optical disc 26. To be placed on the surface 70 with information. This is done by driving the inductor 52 in response to an error signal, such that the point of impact of the read beam 22 is directed to the surface 70 of the optical disc 26, as indicated by arrow 86 shown in FIG. To the desired position in the circumferential direction.

After the readout beam 22 is reflected from the mirror 42 as the reflected beam 96, it collides with the incident aperture 58 of the objective lens 54, and the information of the optical disc 26 by the lens 54. Is focused to a spot on one of the tracks 66 with. The objective lens 54 is used to make the readout beam a spot of light of a desired size at the point where the readout beam 22 impinges on the surface 70 with the information of the optical disc 26. It is desirable for the readout beam 22 to completely fill the incident aperture 58, resulting in a higher intensity of light at the point of impact with the disk 26.

The optical system 10 thus directs the read beam 22 to the optical disc 26 and focuses the read beam 22 at the spot where it collided with the optical disc 26. In the normal reproduction mode, the focused read beam 22 impinges on the light reflecting areas 74 arranged successively and the light non-reflecting areas 78 representing the information stored on the disc 26. The reflected light is collected by the objective lens 54 to produce the reflected portion of the readout beam. This reflected beam 96 returns back to the previously described path by successive collisions with the mirror 42 and the quarter wave plate 38, where the quarter wave plate 38 adds 45 degree polarization rotation to the resulting beam. This results in a total rotation of 180 degrees of polarization. The reflected read beam 96 then impinges on the beam splitting prism 34, which turns the propagation direction of the portion 98 of the reflected read beam so that the signal recovery sub shown in FIG. Collisions in part of system 104.

3 is a schematic block diagram of a portion of the signal recovery subsystem 104. The signal recovery subsystem 104 receives the beam 98 and generates a plurality of information signals. These signals are then provided to various parts of the optical disc player. These information signals are generally classified into two types, and the information signal itself represents a control signal obtained from stored information and an information signal for controlling various parts of the optical disc player. This information signal is a modulation signal representing information stored on disk 26 and provided to a signal processing subsystem (not shown). The first type of control signal generated by the signal recovery subsystem 104 is a differential focus error signal provided to a focus servo system (not shown). The second type of control signal generated by the signal recovery subsystem 104 is a differential tracking error signal. This differential tracking error signal is provided to the tracking servo subsystem 94 which drives the inductor 52 to move the read beam 22 in the radial direction.

To receive the reflected beam 98, the signal recovery subsystem 104 may include a first tracking photodetector 112, a second tracking photodetector 116, and an inner portion 122 and an outer portion 123. A diode detector array 108 including a concentric ring detector 120 having both. The signal recovery subsystem 104 includes a first tracking preamplifier 124, a second tracking preamplifier 128, a first focus preamplifier 132, a second focus preamplifier 136, and a first differential amplifier 140. ), And a second differential amplifier 144. The first and second tracking preamplifiers 124 and 128, together with the first differential amplifier 140, constitute the tracking signal processor 146 of the signal recovery subsystem 104.

Diode detector array 108 has first, second, third, and fourth outputs 148, 152, 156, 160. The first output 148 is electrically connected to the input terminal 164 of the first tracking preamplifier 124, and the second output 152 is electrically connected to the input terminal 168 of the second tracking preamplifier 128. The third output 156 is electrically connected to the input terminal 172 of the first focus preamplifier 132, and the fourth output 160 is electrically connected to the input terminal 176 of the second focus preamplifier 136. Is connected. The first tracking preamplifier 124 has an output terminal 180 electrically connected to the first input terminal 182 of the first differential amplifier 140, while the second tracking preamplifier 128 has a first differential amplifier ( And an output terminal 184 electrically connected to the second input terminal 186 of 140. The first focus preamplifier 132 has an output terminal 188 electrically connected to the first input terminal 190 of the second differential amplifier 144, while the second focus preamplifier 136 has a second differential amplifier ( And an output terminal 192 electrically connected to the second input terminal 194 of 144.

The reflected beam 98 comprises three parts: a first tracking beam 196 impinging on the first tracking photodetector 112; A second tracking beam 197 impinging on the second tracking photodetector 116; A central information beam 198 impinging on the concentric ring detector 120. The signal generated by the first tracking photodetector 112 is provided to the first tracking preamplifier 124 via the first output terminal 148 of the diode detector array 108. The signal generated by the second tracking photodetector 116 is provided to the second tracking preamplifier 128 via the second output terminal 152 of the diode array 108. The signal generated by the inner portion 122 of the concentric ring detector 120 is provided to the first focus preamplifier 132 via the third output terminal 156 of the diode array 108, while the concentric ring The signal generated by the outer portion 123 of the detector 120 is provided to the second focus preamplifier 136 via the fourth output terminal 160 of the diode array 108.

The output from the first differential amplifier 140 is a differential tracking error signal, which is applied to the tracking servo system 94 described in more detail below. The output from the second differential amplifier 144 is a differential focus error signal applied to a focus servo system, not shown. Although the invention of the present application is described with reference to the signal recovery subsystem 104 just described, other signal recovery subsystems known in the art may be used.

The function of the tracking servo subsystem 94 is to cause the read beam 22 to collide straight on the center of the information track 66. Read beam 22 is generally the same width as a series of indicia with information forming information track 66. When all or most of the read beam 22 is moved to impinge on the light reflecting and light non-reflecting regions 74 and 78 disposed successively on the information track 66, maximum signal recovery is achieved. The tracking servo subsystem 94 is often referred to as a radial tracking servo in the radial direction since the departure from the information track 66 in the radial direction of the disk surface 70 most often occurs. The radial tracking servo 94 can generally operate continuously in the normal playback mode of the optical disc player.

The tracking servo subsystem 94 is shown in more detail in FIG. 4 and includes a loop interrupt switch 200 and an amplifier 202 for driving the inductor 52. The loop interrupt switch 200 receives a tracking error signal from the signal recovery subsystem 104 at the first input 204 and a loop interrupt signal at the second input 206. If the loop interrupt signal is not active, a tracking error signal is provided to its output stage 208. The amplifier 202 receives a tracking error signal at its input 210 and generates a tracking A signal for the inductor 52 at the first output 212 and for the inductor 52 at the second output 214. Generate a tracking B signal. The tracking A signal and the tracking B signal together control the radial movement of the readout beam. When a tracking error signal is received at the input 210 of the amplifier 202, these two tracking signals control the current through the inductor 52 such that the collision of the read beam 22 is moved in the radial direction and the read beam 22 In the center of the information track illuminated by). The direction and magnitude of the movement is determined by the polarity and amplitude of the tracking error signal.

In certain modes of operation, tracking servo subsystem 94 is interrupted such that tracking error signals generated from signal recovery subsystem 104 are not provided to amplifier 202. One operation of this mode is a search operation, when it is desirable for the focused read beam 22 to traverse a portion of the information bearing portion of the disk 26. In this mode of operation, an interrupt signal is provided to the second input 206 of the interrupt switch 200 and the tracking servo system 94 such that the switch 200 is provided with a tracking error signal at its output 208. To prevent it. In addition, in a jump-back mode operation in which the focused read beam 22 jumps from one track to an adjacent track, no tracking error signal is provided to the amplifier 202. In jump-back mode, the amplifier 202 does not provide tracking A and tracking B signals, which makes it easy for them to destabilize the radial beam deflection means, indicated by the inductor 52, and then to proper tracking in adjacent information tracks. This is because the radial tracking servo subsystem 94 needs a longer period of time to obtain again. In general, in a mode of operation in which the tracking error signal is removed from the amplifier 202, a replacement pulse is generated that gives the amplifier 202 a clean and clear signal to move the read beam to the next designated position. A cross-sectional view taken in the radial direction across the optical disc 26 is shown in line A of FIG. 5, which shows a plurality of information tracks 66 and a plurality of inter-track regions 224. The intertrack regions 224 are similar to the light reflecting regions 74 shown in FIG. 2. The lengths of the lines indicated at reference numerals 228 and 232 indicate the inter-track center-to-center spacing between center track 236 and the first track adjacent thereto and between the center track 236 and the second track adjacent thereto, respectively. The point indicated by reference numeral 248 in line 228 and the point indicated by reference numeral 252 in line 232 indicate the branch points between the central track 236 and adjacent tracks 240 and 244, respectively. Each of the branch points 248 and 252 is exactly intermediate between the central track 236 and the first and second tracks 240 and 244. The point indicated at reference numeral 256 on the line 228 indicates the center of the first information track 240, while the point indicated at reference numeral 260 on the line 232 indicates the center of the second information track 244. The point indicated at 264 indicates the center of the central information track 236.

Typical optical discs contain approximately 11,000 tracks per inch. The distance between the center of one information track and the next adjacent information track is on the order of 1.6 microns, while the information display aligned to a particular information track is approximately 0.5 microns wide. This leaves approximately 1 micron of empty open space between the outermost regions of the indication located in adjacent information tracks.

When the read beam 22 deviates from the center of the information track 66, the intensity of the reflected signal received by either the first tracking photodetector 112 or the second tracking photodetector 116 increases, while the other The intensity of the reflected signal received by the photodetector is reduced. Which photodetector receives more or less intensity signals depends on the direction in which the read beam 22 deviates from the center of the information track 66. The phase difference between the signals provided from the first and second tracking photodetectors 112 and 116 represents a tracking error signal. The tracking servo subsystem 94 operates to receive signals from the first and second tracking photodetectors 112 and 116 and minimize the difference between them to direct the read beam 22 to the center of the information track 66. Let's stay on.

The differential tracking error signal generated by the first differential amplifier 140 is shown in line B of FIG. 5 and is an indication of the radial position of the read beam 22 on the disk 26. The differential tracking error signal output has a first maximum tracking error at the point indicated at reference numeral 268 in the middle of the center information track 236 and the branch point 248, and the center and branch points 252 of the center information track 236. Has a second maximum tracking error at the point indicated at reference numeral 272 in the middle of the figure. The third maximum tracking error appears at the point indicated at reference numeral 276 in the middle of the first information track 240 and the branch point 248, and the fourth maximum tracking error is at the center and the branch point of the second information track 244. It appears at the point indicated at reference numeral 280 in the middle of (252). Minimal tracking errors appear at points 284, 288, and 292 corresponding to the centers of information tracks 240, 236, and 244, respectively. Minimal tracking errors also appear at points 296 and 298 corresponding to each of branch points 248 and 252.

The tracking signal processing unit 300 of the signal processing subsystem 104 of the present invention is shown in FIG. The tracking signal processor 300 receives tracking error signals from both the first tracking photodetector 304 and the second tracking photodetector 308 of the diode array 312 similar to the diode array 108 described with reference to FIG. 3. Receive. Although not shown, the processor 300 may receive tracking error signals from other types of photodetectors such as a dual photodetector. The tracking signal processor 300 may include a first preamplifier 316, a second preamplifier 320, a first operational amplifier 324, a second operational amplifier 328, a first analog multiplier 332, and a first preamplifier 316. Two analog multipliers 336 and a summing amplifier 320. The tracking signal processor 300 includes a third operational amplifier 348, a feedback loop compensation circuit 352, a phase shifter 356, and first and second sine function generators 360 and 364. It further includes a local feedback loop 344. Phase shifter 356 provides an offset voltage that results in a phase shift between the outputs of sine function generators 360 and 364.

The first preamplifier 316 has an input terminal 368 and an output terminal 372, and the second preamplifier 320 has an input terminal 376 and an output terminal 380. The first operational amplifier 324 is a positive first input terminal 384 electrically connected to the output terminal 372 of the first preamplifier 316, and a negative second input terminal electrically connected to the positive power supply 392. 388 and output terminal 396. The second operational amplifier 328 includes a positive first input terminal 400 electrically connected to the output terminal 380 of the second preamplifier 320, and a negative second input terminal electrically connected to the power supply 392. 404 and output terminal 408.

Referring to the feedback unit 344 of the tracking signal processing unit 300, the third operational amplifier 348 has an input terminal 412 and an output terminal 416. The phase compensation circuit 352 has an input terminal 420 and an output terminal 424 electrically connected to the output terminal 416 of the third operational amplifier 348. Phase shifter 356 has an input terminal 428 and an output terminal 432 electrically connected to output terminal 424 of phase compensation network 352. The first sine function generator 360 has an input terminal 436 and an output terminal 440 electrically connected to the output terminal 432 of the phase shifter 356, while the second sine function generator 364 has a phase It has an input terminal 444 and an output terminal 448 electrically connected to the output terminal 424 of the compensation network 352.

The first analog multiplier 332 is electrically connected to the first input terminal 452 and the output terminal 440 of the first sine function generator 360, which are electrically connected to the output terminal 396 of the first operational amplifier 324. Has a second input terminal 456 and an output terminal 460 connected to each other. The second analog multiplier 336 is electrically connected to the first input terminal 464 and the output terminal 448 of the second sine function generator 364, which are electrically connected to the output terminal 408 of the second operational amplifier 328. Has a second input terminal 468 and an output terminal 472 connected to each other. The summing amplifier 340 is electrically connected to the first input terminal 476 electrically connected to the output terminal 460 of the first analog multiplier 332 and the output terminal 472 of the second analog multiplier 336. And an output terminal 484 electrically connected to both the input terminal 412 of the second input terminal 480 and the third operational amplifier 348 and the tracking error subsystem 94.

The first preamplifier 316 receives the tracking signal output from the first tracking photodetector 304 at its input terminal 368, while the second preamplifier 320 has a second at its input terminal 376. The tracking signal output from the tracking detector 308 is received. These two tracking signals are periodic signals if plotted as a function of radial position along the disk 26 surface, and these two signals are approximately 90 degrees out of phase. The tracking signals output from the two tracking detectors 304, 308 are amplified and then provided to the output terminals 372, 380 of the first and second preamps 316, 320, respectively.

The first operational amplifier 324 which receives the amplified tracking signal from the first preamplifier 316 at the positive input terminal 384 and the positive voltage at the negative input terminal 388 is the common mode voltage of the tracking signal. common mode voltage) and provide a substantial portion of the signal corresponding to the tracking error signal at its output terminal 396. The second operational amplifier 328, which receives the amplified tracking signal from the second preamplifier 320 at the positive input terminal 400 and receives the positive voltage at the negative input terminal 404, has a common mode voltage (a) of the tracking signal. common mode voltage) and provide a substantial portion of the signal corresponding to the tracking error signal at its output terminal 408.

The first multiplier 332 multiplies the tracking signal received from the output terminal 396 of the first operational amplifier 324 with the feedback signal received from the output terminal 440 of the first sine function generator 360. The resulting modified tracking signal is provided to the output terminal 460 of the multiplier 332. The second multiplier 336 multiplies the tracking signal received from the output terminal 408 of the second operational amplifier 328 with the feedback signal received from the output terminal 448 of the second sine function generator 364. The resulting modified tracking signal is provided to output terminal 472 of multiplier 336.

The summation amplifier 340 receives modified tracking signals from the first and second multipliers 332, 336 at its first and second input terminals 476, 480, respectively. Upon receiving these signals, summing amplifier 340 adds them logarithmically to generate a differential tracking error signal representing the phase difference between these two modified tracking signals. The differential tracking error signal is provided to the output terminal 484 of the amplifier 340. The tracking error signal is then provided not only to the interrupt switch 200 of the tracking servo subsystem 94 (FIGS. 1 and 4) but also to the feedback unit 344 of the tracking signal processing unit 300.

The feedback unit 344 of the tracking signal processor 300 receives the differential tracking error signal from the first input terminal 412 of the third operation or feedback amplifier 348. The feedback amplifier 348 amplifies the tracking error signal using a predetermined loop gain and provides this amplified signal to the input terminal 420 of the feedback loop compensation circuit 352. The feedback loop compensation circuit 352 provides phase gain compensation for the amplified tracking error signal and sends this signal to the input terminal 444 of the second sine generator 364 and to the input terminal 436 of the phase shifter 356. to provide.

The phase shifter 356 is configured such that a signal provided to the input terminal 436 of the first sine function generator 360 and a signal provided to the input terminal 444 of the second sine function generator 364 are mutually designated by a predetermined voltage. To do otherwise, a predetermined voltage offset is provided to the tracking error signal received at its input terminal 428. The voltage offset introduced by the phase shifter 356 is selected to have a voltage value that causes the output of the two sine function generators 360, 364 to have a 90 degree phase difference from each other. The effect of this phase shift is that if the signal provided to the output terminal 440 of the first sine function generator 360 acts on the signal provided to the output terminal 424 of the phase compensation network 352, Is equal to the signal provided by the cosine generator. Accordingly, the signals output from the first and second sine function generators 360 and 364 have a 90 degree phase difference. While a phase difference of substantially 90 degrees is desired, the present invention can also be performed using other phase differences within the range of about 30 degrees. Accordingly, the phase angle may be in the range of about 60 degrees to about 120 degrees. If the phase difference of the signals at the output terminals 440 and 448 is too large, this system will be unreliable.

Both first and second sine function generators 360, 364 can be spherical by various methods known in the art. One of these implementations is shown in FIG. 7 shows an A / D converter (analog-to-digital converter, 488), a ROM look-up table 490 with a plurality of stored sine values and a D / A converter (digital-to-analog). A sine function generator that includes a transformer 492. The signal provided to the input terminal of the sine function generator is first converted into a digital signal by the converter 488, and the ROM 490 receives this digital signal at its input terminal 494 and corresponds to its output terminal 496. Generates a function value. This sine function value is converted into an analog signal by the converter 492 and provided to the output terminal of the sine function generator.

The signal recovery subsystem 104 (FIG. 3), when working with the tracking signal processor 300 of the present invention, continues to provide tracking error signals to the tracking servo subsystem 94 (FIGS. 1 and 4). This tracking servo subsystem 94 uses a tracking error signal to drive the inductor 52 in the manner described above to control the radial position of the read beam 22. Accordingly, the tracking servo subsystem 94 keeps the read beam 22 centered on the information track 66.

The tracking servo subsystem 94 uses the provided tracking error signal in the same way regardless of the tracking signal processor 300 used in the signal recovery subsystem 104, while the use of the tracking signal processor 300 This results in another tracking error signal being provided to the tracking servo subsystem 94. When the tracking signal processing unit 300 is used, the provided tracking error signal remains periodic, but the use of the tracking signal processing unit 300 causes each period of the tracking error signal to indicate the position of a wider area on the optical disc 26. cause.

8 shows a comparison of tracking error signals, each of which is a function of radial position over a portion of the disc 26. Signal 512 is a tracking error signal generated by signal recovery subsystem 104 using prior art tracking signal processing section 146, while signal 516 uses tracking signal processing section 300 of the present invention. Is a tracking error signal generated by the signal recovery subsystem 104. Since the tracking error signal 516 is substantially linear in the region near the value whose value is halfway between the maximum values, it can be said that the tracking signal processing unit 300 linearizes the tracking error signal. However, signal 516 remains periodic, as can be seen in FIG. 9, which represents the signal 516 value for the wider portion of disk 26. In the case where the tracking signal processing unit 146 is used, each period of the tracking error signal 512 represents one information track 66 of the disc 26. However, when the tracking signal processing unit 300 is used, each period of the tracking error signal may be made to represent any number of information tracks 66.

The number of information tracks represented in each period of the tracking error signal 516 is determined by the gain of the feedback amplifier 348. There are advantages to linearizing a large number of tracks 66. For example, after local feedback loop 344 operates to linearize the tracking error transmission characteristic for several tracks, a noise pulse with a magnitude greater than one track is still present in the negative slope of the linearized error signal. Within the operating range, this allows a normal response by tracking error subsystem 94 for such noise pulses. However, because the amplitude of the signal 516 is finite, the larger the number of tracks shown in each period, the smaller the voltage difference between each track 66. If the voltage difference between adjacent tracks 66 is too small, it will be difficult to distinguish the tracks 66, resulting in a tracking error. Therefore, there is a functional track-off when selecting the number of tracks indicated by each period of the tracking error signal 516.

Tracking servo 94 should operate within the negative feedback slope of tracking error signal 516. This is because the tracking servo 94 drives the inductor 52 to move in the direction in which the beam 22 increases the tracking error if a positive tracking error signal is provided. Tracking errors will continue to accumulate and cause malfunctions. This is also true for the response of the tracking servo to the tracking error signal 512. However, within the feedback section 344 of the tracking signal processing section 300, the use of positive feedback does not cause any such problem. This is because the tracking signal processing unit 300 is always placed on the tracking error signal 516 of negative slope, regardless of whether self-correction is first provided with a positive feedback signal.

The values of the tracking signals provided by the first and second tracking photodetectors 304, 308 are taken together to indicate the relative radial position of the read beam 22 on the disc 26. In addition, the value of the signal provided to the feedback 344 of the tracking signal processor 300 indicates a feedback position in a relative radial direction. The use of feedback section 344 minimizes the difference between the values of these two signals. Accordingly, the tracking signal processing unit 300 may use the feedback unit 344 to restore the tracking error signal to near zero, which is a value indicating a position in a specific radial direction on the disk 26. This may cause tracking servo system 94 to stabilize read beam 22 and impinge on desired information track 66.

The signals provided by the first and second tracking photodetectors 304, 308 are both periodic and have a phase difference of approximately 90 degrees. They can be represented by sine and cosine functions.

For the following discussion, assume that the photodetector has two signal outputs in quadrature. The signal provided to the first preamplifier 316 by the first tracking photodetector 304 is defined as sin (x) and provided to the second preamplifier 320 by the second tracking photodetector 308. The signal is defined as sin (x + 90) or cos (x). Where x is the position in the relative radial direction of the readout beam 22. The signal provided to the second input terminal 468 of the second multiplier 336 is defined as sin (y), and the signal provided to the second input terminal 456 of the first multiplier 332 is sin (y + 90). ) Or cos (y). Where y is the value of the relative radial feedback signal. Under this definition, the signal at the output terminal 460 of the first multiplier 332 is sin (x) cos (y) and the signal at the output terminal 472 of the second multiplier 336 is cos (x). sin (y). Accordingly, the signal at output 484 of summing amplifier 340 is:

a [sin (x) cos (y)-cos (x) sin (y)] = asin (x-y) ≒ a (x-y)

Where a is the gain rate constant. As is known in the art, for values of x-y close to zero, sin (x-y) is approximately x-y. Therefore, for x-y values close to zero, the tracking error signal a (sin (x-y)) is substantially linear. The relationship of x and y can be adjusted for a given application by setting the gain of feedback amplifier 348 appropriately.

In a particular embodiment of the invention, the second sine function generator 364 may be replaced with a cosine function generator, which receives the signal provided to the output terminal 424 of the phase compensation network 352. The use of a cosine function generator in this embodiment eliminates the need for using phase shifter 356.

6, 10, 11, and 12, in a particular embodiment of the invention, the inputs of the amplifiers 316, 320 are optical pickup links that include an optical subsystem represented herein as a prism 520. It is formed by. The source beam 524 passes through the lens 526 and is received by a conventional interferometer 528 having a plate that separates the source beam into two beams 530, 532, which are mirrors 534, 536, respectively. The prism 520 and portions of the interferometer 528 may be moved relative to each other in the direction indicated by the two-way arrow 522. As a result of the relative movement, the fringe patterns formed by the interferometer change. The reflected beams are recombined as beam 538 and collimated by lens 540. Beam 538 then reaches receiver / analyzer 542. Fringe patterns propagated into the beam 538 are measured by a quadrature photodetector 546, which may be a ring photodetector and is typically disposed within the receiver / analyzer 542. The analog outputs 548, 550 of the photodetector 546 are then provided to the preamps 316, 320 (FIG. 6).

Referring again to FIGS. 1 and 3, the above-described embodiments are disclosed to result in an error signal for the servo circuit; However, in some applications, i.e., applications which only need to measure the position or other characteristic of the object, the error signal generated by the signal processing unit 146 does not need to be provided to the servo circuit, and other users of this information, For example, it can be connected to a computer or a measurement indicator. In this case, the beam deflection means indicated by the tracking servo 94 and the inductor 52 can be omitted.

An implementation of the circuit shown in FIG. 6 is disclosed with reference to FIG. 13. The tracking signals 544 and 546 received from the photodetectors of the optical pickup link are generally orthogonal to each other and are connected to input terminals of the differential amplifiers 548 and 550 respectively. The outputs of the differential amplifiers 548, 550 represent the differences between their input signals 548, 550 and the offset voltage generated by the voltage divider 552, respectively. The outputs of the differential amplifiers 548, 550 are input to the multipliers 554, 556, respectively.

The function generator 558 generates a cosine function output 560 and a sine function output 562 applied to the second input terminals of the multipliers 554 and 556, respectively. Summing amplifier 564 receives the outputs of multipliers 554 and 556 and generates tracking signal 566. Tracking signal 566 is connected back to the optical pickup for insertion into the servo tracking loop via connector 568. Tracking signal 566 is also connected to potentiometer 570, which adjusts the local feedback loop gain. From potentiometer 570, tracking signal 566 is coupled to compensation circuit 572, for the purpose of providing phase and gain compensation to maintain loop stabilization. The function generator 558 receives a first input 574 from a compensation circuit 572 and a second grounded input 576.

14 shows the function generator 558 in detail. A / D converter 580, preferably AD779KN, receives inputs 574, 576, and FIG. 13 and supplies two structurally identical units, denoted by reference numerals 585 and 595. Unit 585 generates a sine function, and unit 595 generates a cosine function. For simplicity, only unit 585 will be described. Output terminals 583 of A / D converter 580 are connected to address lines 587 of erasable and programmable memory 582. In this embodiment A / D converter 580 has a higher bit resolution than necessary, and the least significant bit position 586 is grounded. Accordingly, outputs 583 provide a vector to erasable and programmable memory 582, and the corresponding sine values are output to data lines 588. The sine value represented by the signal on lines 588 is then converted to an analog signal at D / A converter 590, which may be AD767KN. The four lowest points 592 of the D / A converter 590 are grounded because the D / A converter has a higher resolution than necessary. Analog output 593 is connected to filter circuit 594, the purpose of which is to weaken the signal to eliminate aliasing.

Unit 595 differs from unit 585 only in that other data sets are stored in its erasable and programmable memory 586 to generate a cosine function. Preferably the data is programmed when 0 volts is input to the units 585, 595 by the A / D converter 580, and the output terminals 597, 598 have a voltage of the same magnitude, preferably 0.7 volts. Have

In programming the erasable and programmable memories 582 and 597, it is necessary for the A / D converter to compensate for generating 2's complementary signals, which signals can be erased and programmable memories 582, It is not continuous or linear as shown by 597). Thus, adjustment of data in memories is necessary to generate correct sine and cosine functions. The computer programs listed in Lists 1 and 2 may be performed to generate suitable data for programming the erasable and programmable memories 582, 597.

Typical timing signals required for the functionality of the integrated circuit in FIG. 14 are provided by timing block 600, which is shown in more detail in FIG. 15. Crystal oscillator 602 operates at 24 mHz and is connected to a counter 604, which may be 74HC4060J. The timing signals formed by block 600 include a chip select signal 606, a chip enable signal 608, an output enable signal 610, and a transform enable signal 612.

List 1

List 2

16-18 illustrate the operation of the embodiment shown in FIG. 13. In FIG. 16, the plurality of tracks 620 to 625 form a region of interest of the optical pickup moving along the path 626. The RF reproduction signal from the read optical disc is shown as waveform 628, where maximum values represent track crossings and minimum values represent regions between tracks. Waveform 630 is a disturbing signal that causes the optical head to deviate from the current track. Waveforms 632 and 634 show the output of the sine and cosine generators on lines 562 and 560 of FIG. 13, respectively. FIG. 17 is similar to FIG. 16, and like waveforms are given like reference numerals. Waveforms 636 and 638 represent the outputs of amplifiers 548 and 550. 18 illustrates operation of the system in response to a forced signal 642 causing the optical pickup to move across seven tracks of the optical disc. Waveform 640 represents an RF reproduction signal. Waveforms 644 and 646 represent the outputs of amplifiers 548 and 550.

Referring now to FIGS. 1, 3, 6, and 19, a focus signal processor 700 of the signal processing subsystem 104 of the present invention is shown in FIG. 19. The structure of the focus signal processing unit is similar to that of the tracking signal processing unit 300 shown in FIG. 6, and elements having similar functions in FIG. 19 are given with the same reference numerals. The objective lens 54 (FIG. 1) is generally driven by the focus drive 702 in a direction perpendicular to the direction of the optical disc 26. As shown in FIG. A known type of photodetector (detector) 712 is associated with the objective lens 54 and responds to the position of the objective lens 54 relative to the ideal focal plane that coincides with the surface of the optical disc 26. The output of the photodetector 712 is connected to the first preamplifier 316 and the second preamplifier 320. Output 484 is provided to focus error servo subsystem 794, which is fed back to focus drive 702. Otherwise, the operation of the focus signal processor 700 is the same as the operation of the tracking signal processor 300, and the description will not be repeated for simplicity.

20 compares the operating characteristics of the system using the embodiment of FIG. 19 with those of the conventional focus control system. The magnitude of the focus error signal is plotted relative to the displacement of the focus of the beam from the desired plane, relative to point 805. The sinusoidal curve represented by the focus error signal 804 of the conventional servo has an available operating range indicated by the dimension "A". The focus error signal 806 indicated by the control device according to the invention is substantially linear in the extended operating range indicated by the dimension "B" larger than the dimension "A". In practice the dimension "B" will be at least twice as large as the dimension "A". Lines 808 and 810 represent the upper and lower limits of the focusing area of a conventional focus control system. Waveform 802 shows the focus error signal over time in a typical application. The amplitudes of waveform 802 exceed the limits defined by lines 808 and 810 so that conventional systems will lose focus lock. The operating range of the focus control system according to the present invention is defined by lines 812 and 814 such that waveform 802 remains within the operating range of the system of the present invention.

Although the present invention has been described with reference to the structures disclosed herein, it is not limited to those described, the application of the present invention includes any modifications and changes that may fall within the scope of the following claims.

Claims (11)

A device for controlling a focused radiant energy beam, An optical element for determining a traveling direction of the focused beam; An actuator acting on the optical element to shift the focus of the focused beam in a direction of a predetermined position; A detector having first and second outputs receiving light from the beam and responsive to displacement of the focal point of the beam from the predetermined position; Circuitry connected to the outputs of the detector to generate an error signal indicative of the displacement of the focal point of the beam from the predetermined position; A servo connected to the actuator and the error signal Wherein the actuator moves the focus of the beam to the predetermined position in response to the servo; The control device is: A local feedback loop connected to the outputs of the detector, the local feedback loop being: A first periodic function generator responsive to the error signal; A second periodic function generator responsive to said error signal, The second periodic function generator has an output different in phase angle from the output of the first periodic function generator; A first multiplier for multiplying the first output of the detector and the output of the first periodic function generator; A second multiplier that multiplies the second output of the detector by the output of the second periodic function generator, And said outputs of said first and second multipliers are provided as inputs of said circuit. According to claim 1, And said periodicity is substantially sinusoidal and said first and second periodic function generators are sinusoidal generators. According to claim 1, And said first and second outputs of said detector are approximately mutually orthogonal with respect to said displacement of said beam, and said phase angle is approximately 90 degrees. According to claim 1, Wherein the first and second outputs of the detector are approximately mutually orthogonal with respect to the displacement of the beam. The method of claim 4, wherein And said phase angle is in a range from about 60 degrees to about 120 degrees. The method of claim 5, And wherein said phase angle is approximately 90 degrees. A method of focusing a radiant energy beam, comprising: Generating first and second detection signals in response to a focal position of the beam; Generating an error signal indicative of the displacement of the focal point from a predetermined position, the error signal being periodic with respect to the displacement; Returning a focal point separated by the displacement to the predetermined position in response to the error signal The method comprising: Generating a first periodic signal in response to the error signal; And Generating a second periodic signal having a phase angle different from that of the first periodic signal in response to the error signal; Generating the error signal includes: Calculating a first product signal by multiplying the first detection signal by the first period signal; Calculating a second product signal by multiplying the second detection signal by the second period signal; And Determining the difference between the first product signal and the second product signal. The method of claim 7, wherein And the first and second detection signals and the first and second periodic signals are substantially sinusoidal. The method of claim 7, wherein Wherein the first and second outputs of the detector are approximately mutually orthogonal with respect to the displacement of the beam, and the phase angle is about 90 degrees. The method of claim 9, And wherein said phase angle is in the range of about 60 degrees to about 120 degrees. The method of claim 10, The phase angle is approximately 90 degrees.