JPH03142721A - Track servo circuit for optical disk device - Google Patents

Abstract

PURPOSE:To enable track control with high accuracy by calculating the average value of respective sample data for a driving signal in the case of control only by a feedback signal and executing reading of data and conversion to an analog signal synchronously with the rotation of an optical disk. CONSTITUTION:A feed forward signal generator 7 is provided and the driving signal of an optical head 1 in the case of control only by the feedback signal is sampled only for one time rotation of the optical disk 1 with a prescribed cycle. Then, analog / digital conversion is executed and for each sample data, the average value is calculated and stored based on an L(=1,2,...) number of the sample data before and behind the objective sample data. Each average value is read out synchronously with the rotation of an optical disk 2 and digital / analog conversion is executed. Then, the average value is outputted as a feed forward signal. Thus, since the phase delay of the feed forward signal is eliminated, track error caused by the track eccentricity of the optical disk is improved and the track control can be executed with high accuracy.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a track servo circuit for controlling the tracking of an optical head of an optical disk device.

(Prior Art) Figure 2 shows an example of a conventional track servo circuit of this type, in which 1 is an optical head, 2 is an optical disk, 3 is a feedback (FB) signal generator, and 4 is a current amplifier. It is.

The optical head 1 is composed of a lens, a lens actuator, a laser diode, a light receiving element, etc., and is held so as to be movable relative to the optical disk 2 in a direction perpendicular to its tracks. The optical disc 2 has concentric or spiral tracks on which arbitrary information is recorded, and is rotationally driven by a drive mechanism (not shown). The FB signal generator 3 is composed of a tracking error detection circuit, a lead-lag filter, etc., and receives the output signal of the optical head 1, generates a tracking error signal, and further widens the servo band by using a lead-lag filter. and outputs it as a feedback (FB) signal.

In the device, a light beam emitted from an optical head 1 is reflected by an optical disk 2 and is received by the optical head 1 again. The received light beam contains any information recorded on the optical disc 2 as well as information associated with tracking errors, focus adjustment errors, etc. The output signal of the optical head 1 is input to the FB signal generator 3, where the above-mentioned FB signal is generated. This FB signal is current-amplified by a current amplifier 4 and is manually input to a lens actuator for track control of the optical head 1. As a result, the lens is displaced in a direction perpendicular to the track, and the track control of the light beam is performed.

However, control using only the FB signal described above has little effect in a high frequency band, and therefore tracking errors cannot be easily reduced.

FIG. 3 shows another example of a conventional track servo circuit in consideration of the above-mentioned points, in which a feedforward (FF) signal generator 5 and an adder 6 are added to the circuit of FIG. The FF signal generator 5 is composed of a low-pass filter, an analog memory, etc., and uses a low-pass filter to remove asynchronous components, that is, high-frequency components, from the drive signal and stores the signal in the analog memory in synchronization with the rotation of the optical disk. Read and output as a feedforward (FF) signal.

Further, the adder 6 adds the FF signal and the above-mentioned FB signal and inputs the result to the current amplifier 4.

According to the circuit, track control is performed in accordance with the movement of the optical head predicted in advance by the FF signal, so the burden on the feedback loop is reduced and the accuracy of track control is improved.

(Problem to be Solved by the Invention) However, in the above circuit, a phase lag occurs in the signal stored in the analog memory due to the low-pass filter in the FF signal generator 5, and as a result, a phase lag occurs in the FF signal itself. Therefore, there was a problem that highly accurate track control was not possible.

Figure 4 shows the optical head drive signal and F in the circuit of Figure 3.
This shows the relationship with the F signal. In the figure, S is the drive signal and C
indicates an FF signal.

In view of the above-mentioned problems, it is an object of the present invention to realize highly accurate track control by generating a feedforward signal without phase delay.

(Means for Solving the Problems) In order to achieve the above object, the present invention provides a track servo circuit for an optical disc device that tracks the optical head of the optical disc device using a signal that is the sum of a feedback signal and a feedforward signal. The drive signal of the optical disc is sampled at a predetermined period for one revolution of the optical disc, and converted into analog/digital data.
, 2, . A track servo circuit of an optical disk device is equipped with a feedforward signal generator that outputs a Sampling and converting from analog to digital,
A track servo circuit of an optical disk device is configured to calculate and store the average value of sample data at the same time in each rotation, and further, in this circuit, each average value of sample data at the same time in each rotation is calculated before and after N ( =
The present invention proposes a track servo circuit for an optical disk device that calculates and stores other average values based on the average values of the following.

(Function) According to the present invention, the drive signal for one revolution of the optical disk when controlled only by a feedback signal is sampled at a predetermined period and converted into a digital value, and for each sample data, the number of samples before and after the drive signal is sampled at a predetermined period. An average value based on the data is calculated and stored, and the average value is read out in synchronization with the rotation of the optical disk, converted into an analog value, and output as a feedforward signal.

Further, according to the present invention, the average value of sample data at the same time in each rotation of the drive signal for the rotation of the optical disk is calculated and stored, and a feedforward signal based on this is output.

Further, according to the present invention, for each average value based on the drive signal for the rotation of the optical disk, another average value based on N values before and after it is calculated and stored, and a feedforward signal based on this is calculated and stored. Output.

(Embodiment) FIG. 1 shows an embodiment of a track servo circuit of an optical disc device of the present invention, and in the figure, the same components as those of the conventional example are denoted by the same reference numerals. That is, 1 is an optical head, 2 is an optical disk, 3 is a feedback (F B) signal generator, 4 is a current amplifier, 6 is an adder, and 7 is a feed forward (F F) signal generator.

The FF signal generator 7 is an analog/digital converter (A/
D converter) 71 and input interface (IF) 7
2, a processing unit (CPU) 73, an output interface (IF) 74, and a digital/analog converter (D/A
converter) 75, an attenuator 76, and an index signal detection circuit 77.

The A/D converter 71 inputs a signal corresponding to the movement of the optical head 1, in this case a drive signal output from the current amplifier 4 to the optical head 1, samples it at a predetermined period, for example, every 20μSee, and converts it from analog to digital. do. The input I/F 72 sends sample data of digital values output from the A/D converter 71 to the CPU 73 . C
The PU73 is configured in advance for each sample data before and after L(
(1°2, . . . ) sample data is calculated and stored, and the stored average value is read out in synchronization with the rotation of the optical disc 2. Output IF74 is C
The average value data read from the PU 73 is sent to the D/A converter 75. The D/A converter 75 performs digital-to-analog conversion of the average value data. Attenuator 7
6 attenuates the analog signal output from the D/A converter 75 to an appropriate level and converts it into a feedforward (FF)
) is sent to the adder 6 as a signal. The index signal detection circuit 77 detects the optical disc 1 from the output signal of the optical head 1.
The index signal output every rotation is detected and the timing is notified to the CPU 73.

Next, the operation of the circuit will be explained. The above-mentioned calculation and storage of the average value is performed off-line.

In a state where only the feedback loop of the circuit is operating, the CPU 73 controls the index signal detection circuit 7.
When the index signal detection notification is received from 7, the operation of the A/D converter 71 is started. A/D converter 7
1 is the drive signal output from the current amplifier 4 at 20 μSe.
Sampled every e and sequentially converts it from analog to digital. The sample data of the digital value is input IF7.
2 to the CPU 73, and all are temporarily stored. When the CPU 73 receives notification of the next index signal detection from the index signal detection circuit 77, it stops the operation of the A/D converter 71.

At this time, the CPU 73 stores a number of sample data corresponding to one rotation of the optical disc. Here, assuming that the rotation speed of the optical disk is 900 rpm, that is, the time required for one rotation is 88.86 m5ec, 3333 sample data are stored.

Next, the CPU 73 calculates and stores an average value based on the sample data before and after each stored sample data. At this time, the average value for data near the beginning and end of the sample data is calculated by extracting data before and after the beginning and end of the sample data, assuming that the beginning and end portions are continuous.

Next, an explanation will be given of the operation when performing track control by generating an FF signal based on the average value of the stored sample data.

When the CPU 73 receives the notification of re-index signal detection from the index signal detection circuit 77, the CPU 73 calculates the average value of the sample data at the same period as the sampling time, that is, 20μSee.
read out sequentially. The average value data is sent to the D/A converter 75 via the output IF 74, and is sequentially converted into digital data.
converted to analog. This analog signal is attenuated to an appropriate level by an attenuator 76 and input to the adder 6 as an FF signal. This FF signal is added to the FB signal by an adder 6, current amplified by a current amplifier 4, and input to a lens actuator for track control of the optical head 1. As a result, the lens is displaced in a direction perpendicular to the track, and the track control of the light beam is performed.

When the CPU 73 receives the notification of the re-index signal detection from the index signal detection circuit 77, the CPU 73 calculates the average value of the sample data at the same period as the sampling time, that is, 20 μsec.
read out sequentially. The data of the average value is sent to the D/A converter 75 via the output IF 74, and is sequentially converted from digital to analog. This analog signal is transmitted through an attenuator 76
The signal is attenuated to an appropriate level and input to the adder 6 as an FF signal. This FF signal is added to the FB signal by an adder 6, current amplified by a current amplifier 4, and input to a lens actuator for track control of the optical head 1. As a result, the lens is displaced in a direction perpendicular to the track, and the track control of the light beam is performed.

When the CPU 73 receives notification of the next index signal detection from the index signal detection circuit 77, it returns the average value data to be read to the first data, performs the same operation as described above, and repeats this process thereafter.

FIG. 5(a) shows the drive signal when only the feedback loop is operating, and FIG. 5(b) shows the feedforward signal generated by the signal generator 7 based on the drive signal. . The small level fluctuations in the drive signal are due to feedback loop control, but the large level fluctuations are due to track eccentricity of the optical disc 2, and the period thereof is equal to the rotation period T1 of the optical disc 2, that is, 86. It becomes 88Ilsec.

According to the above embodiment, since the average value of each sample data of the drive signal is taken, fine level fluctuations are smoothed out, and the readout and D/A of data stored in synchronization with the rotation of the optical disk is Since the conversion is performed, there is no phase delay and an FF signal as shown in the figure can be obtained. Therefore,
If the optical head 1 is track-controlled by adding the FF signal to the FB signal, tracking errors caused by track eccentricity of the optical disc 2 can be greatly improved.

FIG. 6 shows how the tracking error is improved according to this embodiment. FIG. 6(a) shows the temporal change in the tracking error during control using only FB signals,
b) shows the temporal change in the tracking error during control using the FB signal and the FF signal.

The above-mentioned eccentricity of the optical disk is mostly caused by the center of the optical disk body being misaligned with the center of rotation when attaching the hub to the disk-shaped optical disk body or when installing the optical disk in the drive. Therefore, all tracks on the optical disk are eccentric by approximately the same amount with respect to the center of rotation. Therefore,
If the average value of the drive signal described above is once calculated and stored off-line when the optical disk is loaded, the tracking error will be improved in the same way as described above even when accessing another track online.

In the embodiment described above, the average value was obtained from sample data for one rotation of the optical disk, but it is also possible to obtain the average value from sample data for M (=1, 2, . . .) rotations.

FIG. 7(a) shows the drive signals sl and S for 5 rotations of the optical disk.
2. S3. Sa and Ss are expressed in the same phase.

These signals S, ~s5 are sampled at a predetermined period and converted into analog/digital signals in the same manner as described above, and the average value of the sample data at the same time in each signal, for example, To in the figure, is calculated, and this is calculated at all times. If this is done, data with the same average value as above can be obtained. FIG. 7(b) shows the <FF signal based on this average value data, and if the FF signal is added to the FB times signal and the optical head 1 is track-controlled, the result is caused by track eccentricity as described above. Tracking errors are significantly improved.

Furthermore, the average value data obtained from the sample data for M rotations mentioned above is calculated for each data item before and after N (=1
, 2, . . . ) average values are calculated and stored, and an FF signal is created based on this, more accurate track control can be performed.

(Effects of the Invention) As explained above, according to the present invention, since the average value of each sample data of the drive signal when controlling only with the feedback signal is taken, the asynchronous component due to the feedback loop is suppressed and the track is tracked. Only the component caused by eccentricity is extracted, and data is read out and converted to an analog signal in synchronization with the rotation of the previous disk, eliminating the conventional phase lag, and thus improving the tracking of the optical disk. Track errors caused by eccentricity are significantly improved, and highly accurate track control can be achieved. In addition, even in cases where the servo band based on the feedback signal cannot be improved due to the presence of mechanical resonance points, it can be effectively supplemented by the feedforward signal, which has the advantage of enabling highly accurate track control. .

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an example of a track servo circuit of an optical disk device of the present invention, FIG. 2 is a block diagram showing an example of a track servo circuit of a conventional optical disk device, and FIG. 3 is a block diagram showing an example of a track servo circuit of a conventional optical disk device. A configuration diagram showing another example of the track servo circuit, FIG. 4 is a diagram showing the relationship between the drive signal of the optical head and the FF signal in the circuit of FIG. 3, and FIG. 5(a)
6(b) is a diagram showing the relationship between the drive signal and the FF signal according to an embodiment of the present invention, and FIGS. 7th
Figures (a) and (b) are other diagrams showing the relationship between the drive signal and the FF signal according to the present invention. DESCRIPTION OF SYMBOLS 1... Optical head, 2... Optical disk, 3... Feedback signal generator, 4... Current amplifier, 6...
Adder, 7...Feedforward signal generator.

Claims (3)

[Claims] (1) In the track servo circuit of an optical disk device that tracks the optical head of the optical disk device using a signal that is the sum of a feedback signal and a feedforward signal, the drive signal for the optical head when controlled using only the feedback signal is equal to one revolution of the optical disk. Sampling is performed at a predetermined period, analog-to-digital conversion is performed, and for each sample data, an average value based on L (=1, 2, ...) sample data before and after it is calculated and stored. 1. A track servo circuit for an optical disc device, comprising a feedforward signal generator that reads out each average value in synchronization with the rotation of an optical disc, converts it from digital to analog, and outputs it as a feedforward signal. (2) Transmit the optical head drive signal to the optical disk M (=1, 2,
(...) A claim characterized in that the number of revolutions is sampled at a predetermined period and converted from analog to digital, and the average value of the sample data at the same time in each revolution is calculated and stored. A track servo circuit for an optical disc device according to item (1). (3) For each average value of sample data at the same time in each rotation, other average values based on N (=1, 2, ...) average values before and after it are calculated and stored. A track servo circuit for an optical disc device according to claim 2, characterized in that: