JPH06103540B2 - Pickup tilt control device - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a tilt control device for a pickup, and more particularly to an optical information recording / reproducing device for optically recording / reproducing information on / from a disc such as a video disc or a digital audio disc. BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pickup tilt control device for controlling the tilt of a pickup used in an apparatus with respect to a disc.

[Outline of Invention]

The present invention relates to a tilt control device for a pickup, which irradiates a disc-shaped information recording medium with light, receives the reflected light, and outputs a light-receiving output signal to control the tilt of the pickup. A vibration signal generating means for outputting, a tilting means for tilting the pickup with respect to the information recording medium in response to the vibration signal, and a light receiving output signal
RF detection means for detecting the envelope of the RF signal and outputting the RF envelope detection signal, comparing the phase of the excitation signal with the phase of the RF envelope detection signal, and comparing means for outputting the comparison signal, and based on the comparison signal A tilt control means for controlling the tilt angle of the pickup and the information recording medium,
While wobbling the pickup, it detects the RF signal and compares the envelope of the RF signal with the envelope of the excitation signal to detect the tilt between the pickup and the disc that is the information recording medium, and thus the angle between the pickup and the disc. Is always maintained at a normal angle.

[Conventional technology]

In order to accurately record and reproduce information in an optical information recording / reproducing apparatus, the light emitted from the light source is tracked to the track on the disc, and the angle between the pickup (optical axis) and the disc is always a predetermined angle. It should be held (ideally approximately vertical). Although there are various methods for tracking control, if the recording / reproducing of information and the tracking control can be performed by one beam, the structure of the pickup can be simplified.

In such a one-beam tracking method, the light receiving means for receiving the reflected light of the light applied to the disk for recording / reproducing information is divided into two right and left with respect to the tangential direction of the track. Output signals from the light receiving element divided into the left and right are as shown in FIGS. 5 (a) and 5 (b), for example. That is, for example, when the level of the signal corresponding to the average light receiving amount between the tracks of the right light receiving element is D,
The level on the track is αD (α is a coefficient).
On the other hand, the signal level (D + ΔD) between the tracks of the light receiving element on the left side and the signal level on the track are β (D + ΔD).
D) (β is a coefficient). If the disturbance of the RF envelope and the fluctuation of the upper side of the RF envelope due to the influence of optical MTF (mechanical transfer function) and the like are ignored, the output R of the right side light receiving means obtained through the low pass filter is as follows.

R = D− (1/4) αD + (1/4) αDe ^{j (ωt + δ)} (1) Further, the output L of the light receiving element on the left side is L = D + ΔD− (1/4) β (D + ΔD) + (1/4) β (D + ΔD) e ^{j (ωt−δ)} ...
(2) Therefore, the tracking error signal E obtained from the difference between the low-pass filters is E = RL−D− (1/4) αD + (1/4) αDe ^{j (ωt + δ)} − {D + ΔD− (1/4) β ( D + ΔD) + (1/4) β (D + ΔD) e ^{j (ωt−δ)} = [D− (D + ΔD) − (1/4) {αD−β (D + ΔD)}] + (1/4) [αDe ^{j (Ωt + δ)} −β (D + ΔD) e ^{j (ωt−δ)} ] (3) Here, ω is the angular frequency when the pickup crosses the track in the disk radial direction, and δ is the phase difference of the diffracted light generated in the left and right light receiving elements. The right side of the equation (3) second
The term includes the phase difference component, and the first term includes the DC offset component.

By the way, as shown in FIG. 6, in a pickup in which the reflected light from the disc 1 is received by the light receiving element 3 via the objective lens 2, when only the objective lens 2 is moved in parallel with the disc 1 and tracking control is performed, the optical axis 4, the position of the chief ray 5 is displaced (the position of the spot 6 on the light receiving element 3 is moved with respect to the two light receiving elements 31 and 32), and the DC component of the equation (3) is changed.

Further, as shown in FIG. 7, when the relative angle between the pickup (optical axis 4) and the disc 1 is inclined, the left and right light receiving elements
The relative light intensity of 31 and 32 changes, and the DC component also changes.

[Problems to be solved by the invention]

Therefore, if the output signals of the light receiving elements 31 and 32 are respectively taken out through a low-pass filter, a tracking error signal is generated from the difference signal, and tracking control is performed, a DC offset occurs in the tracking error signal, and accurate tracking servo is realized. I couldn't. The offset in the case shown in FIG. 6 can be prevented by driving not only the objective lens 2 but also the entire pickup in the tracking direction. For that purpose, it is necessary to reduce the size and weight of the entire pickup. However, there is a limit to downsizing and weight saving, and even if the whole is driven, the offset caused by the disc tilting with respect to the pickup as in the case shown in FIG. 7 is prevented. I can't.

[Means for solving problems]

In order to solve the above problems, the present invention provides a pickup tilt control device for irradiating a disc-shaped information recording medium with light, receiving the reflected light, and controlling the tilt of a pickup that outputs a light reception output signal. Excitation signal generating means for generating and outputting an excitation signal of a predetermined frequency, tilting means for tilting the pickup with respect to the information recording medium in response to the excitation signal, and an RF signal from the received light output signal RF detection means for detecting the envelope and outputting the RF envelope detection signal, comparing the phase of the excitation signal and the phase of the RF envelope detection signal, comparing means for outputting a comparison signal, and based on the comparison signal And a tilt control means for controlling the tilt angle of the pickup and the information recording medium.

[Action]

According to the present invention, the vibration signal generation means generates a vibration signal of a predetermined frequency and outputs the vibration signal to the tilting means and the comparing means, and the tilting means makes the pickup disc-shaped in response to the input vibration signal. Tilt with respect to the information recording medium.

In parallel with this, the RF detection means detects the envelope of the RF signal from the light reception output signal of the pickup and outputs the RF envelope detection signal to the comparison means.

As a result, the comparison means compares the phase of the excitation signal with the phase of the RF envelope detection signal and outputs the comparison signal to the tilt control means.

As a result, the tilt control means controls the tilt angle between the pickup and the information recording medium based on the comparison signal.

〔Example〕

 Next, preferred embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram of an optical information recording / reproducing apparatus of the present invention. In the figure, 11 and 12 are high-pass filters, which extract their high-frequency components from the outputs of the light-receiving elements 31 and 32 that are divided into left and right with respect to the track and the tangential direction. The outputs of the high-pass filters 11 and 12 are supplied to the adder circuit 13 and added, and the added output is further supplied to the detection means 14. The comparison means 16 is adapted to compare the envelope signal of the RF signal output by the detection means 14 with the excitation signal of a predetermined frequency output by the generation means 17. Reference numeral 18 denotes a tilting means for tilting (wobbling) the pickup with respect to the disk at a predetermined frequency in response to the vibration signal. 21, 22
Is a low-pass filter, which extracts low-frequency components from the outputs of the light receiving elements 31 and 32, respectively. Low pass filter 21, 22
Is output to the subtraction circuit 23. Reference numeral 19 denotes a tracking control means, which controls the pickup in the direction perpendicular to the track with respect to the output of the subtraction circuit 23. Reference numeral 20 denotes a tilt control means, which adjusts the tilt angle of the pickup with respect to the disc in accordance with the output of the comparison means 16.

Next, the operation will be described. The light beam emitted from the light source enters the objective lens and is converged on the disc. The light beam reflected by the disc passes through the objective lens and is received by the light receiving element 3
Irradiated on. Since the amount of reflected light is changed by being modulated by pits or the like on the disk, the information signal can be reproduced by demodulating the added output of the light receiving elements 31 and 32. At this time, the signals output from the light receiving elements 31 and 32 are supplied to the high-pass filters 11 and 12 to extract their high frequency components,
An addition circuit 13 adds the signals to obtain an RF signal. This RF
The signal is input to the detection means 14 and its envelope is detected. The envelope signal is input to the comparison means 16.
The output signals of the light receiving elements 31 and 32 are also supplied to the low pass filters 21 and 22, and their low frequency components are extracted. The subtraction circuit 23 generates a tracking error signal from the difference between the low frequency components. The tracking control means 19 controls the tracking of the pickup with respect to the tracking error signal.

Assuming that the DC component of the tracking error signal is E ₁ , E ₁ = D− (D + ΔD) − (1/4) {αD−β (D + ΔD)} (4) from the equation (3) . The coefficients α and β do not change when only the objective lens is moved, like the average amount of light received by the light receiving elements 31 and 32, but when the disc tilts with respect to the pickup, as shown in FIG. Change to α'and β '. Therefore, the output signals obtained through the low-pass filters 21 and 22 of the light receiving elements 31 and 32 change as shown in FIGS. 2 (a), (b) to (c), (d), respectively.

On the other hand, the peak value of the envelope of the RF signal detected by the detection means 14 hardly changes by the movement of only the objective lens, but when the relative angle between the disk and the pickup changes, the peak value of the coefficient α shown in FIG. It changes according to the characteristic that β is combined.

In an ideal state, the RF signal (Fig. 4 (a)) and the tilt error signal (Fig. 4 (b)) corresponding to the tilt angle have the relationship shown in Fig. 4. Now, assuming that the entire pickup is driven by the tracking control means 19, the DC offset of the tracking error signal changes only when the relative angle between the disc and the pickup changes. When the relative angle deviates from the ideal state when the pickup is in the neutral position, the envelope level of the RF signal changes as shown by the broken line in FIG. 4 (a). The direction of change of the envelope of the RF signal has a constant relationship with the tilting direction of the pickup by the tilting means 18. Further, the amount of change can be defined by a characteristic curve obtained by combining the coefficients α and β. Therefore, the comparison circuit 16 uses the excitation signal output from the generation means 17 and the detection means 14
Compare the phase of the envelope signal of the RF signal output by
It outputs a signal corresponding to the direction and amount of change in the RF signal envelope. This signal is input to the tilt control means 20,
The tilt angle of the pickup with respect to the disc is adjusted.

〔effect〕

As described above, the present invention provides a pickup tilt control device for tilt controlling a pickup which irradiates a disc-shaped information recording medium with light, receives the reflected light, and outputs a light reception output signal. And a tilting means for tilting the pickup with respect to the information recording medium in response to the vibration signal, and an RF envelope detection signal by detecting the RF signal envelope from the received light output signal. RF detection means, phase of excitation signal and RF
Comparing means for comparing the phase of the envelope detection signal and outputting the comparing signal; and tilt controlling means for controlling the tilt angle of the pickup and the information recording medium based on the comparing signal,
Since wobbling the pickup, the RF signal is detected, and the inclination of the pickup and the disc that is the information recording medium is detected by comparing the envelope of the RF signal with the envelope of the excitation signal. The tracking servo can be realized and the angle between the pickup and the disc can be always maintained at a normal angle.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram of an optical information recording / reproducing apparatus of the present invention, FIGS. 2 and 4 are waveform diagrams thereof, FIG. 3 is a characteristic diagram thereof, and FIG. Waveform diagram of optical information recording and reproducing device,
6 and 7 are a schematic side view and a plan view of the pickup. 1 ... Disc, 2 ... Objective lens 3, 31, 32 ... Light receiving element, 4 ... Optical axis 5 ... Main beam, 6 ... Spot 11, 12 ... High-pass filter 13 ... Addition circuit, 14 ... Detecting means 16 ...... Comparison means 17 ...... Generating means 18 ...... Tilting means 19 ...... Tracking control means 20 ...... Tilt control means 21, 22 ...... Low pass filter 23 ...... Subtraction circuit

Claims (1)

[Claims] 1. A disk-shaped information recording medium is irradiated with light,
A pickup tilt control device that controls the tilt of a pickup that receives the reflected light and outputs a received light output signal, in a pickup tilt control device that generates and outputs a vibration signal of a predetermined frequency, and corresponds to the vibration signal. And tilting means for tilting the pickup with respect to the information recording medium, and detecting the envelope of the RF signal from the received light output signal to detect RF.
RF detection means for outputting an envelope detection signal, comparing the phase of the excitation signal and the phase of the RF envelope detection signal, comparing means for outputting a comparison signal, the pickup and the information based on the comparison signal A tilt control device for controlling a tilt angle of a recording medium, and a tilt control device for a pickup.