JP2002288851A - Focus offset setting method for optical disk drive - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a focus offset setting method for an optical disk drive which can correct the variations in the offset amount of focus error signals caused by the variation of luminous power and always set the most adequate offset amount of focus error signals. SOLUTION: A focus error signal offset adjusting means and a nonvolatile memory 2 are provided. Inclination data and intercept data, which are the data for adjusting the focus offset, are stored in the nonvolatile memory 2, and a focus offset setting value corresponding to the luminous power of a laser diode at the time of data writing is computed by using the data stored in the nonvolatile memory 2.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a disk-shaped recording medium, for example, a CD-R / RW or a DVD-RAM / + R.
The present invention relates to a method of setting a focus offset in an information reproducing / recording apparatus for a writable recording medium such as W.

[0002]

2. Description of the Related Art CD-R / RW and DVD-RAM / + R
In an optical disk device corresponding to a writable recording medium such as W, in order to reproduce data recorded on a signal surface of a disk or to record data on a signal surface of a disk,
It is necessary to irradiate the laser beam to the signal surface of the disc via an optical system including an objective lens and the like. Further, for accurate data reproduction, tracking control and focus control of the optical head are performed. Normally, in an optical disk device corresponding to several types of disks having different reflectivities, the offset amounts of the tracking error signal and the focus error signal are switched in order to make the reproduction light from each disk appropriate. CD-R / RW and DVD-RAM /
In an optical disk device compatible with a writable recording medium such as + RW, it is necessary to increase the laser beam output at the time of writing data to the recording medium as compared with the time of data reproduction for detecting reflected light from the recording medium. Even in an optical disk device that does not support several types of disks having different reflectivities as described above, it is necessary to provide at least two types of offset amounts of the tracking error signal and the focus error signal for data reproduction and data recording.

[0003]

However, as described above, when the laser light output is increased at the time of writing data to a recording medium, a laser diode (hereinafter, referred to as L) as a light source.
There is a problem that the temperature change of D) occurs, and as a result, the wavelength of the laser light emitted from the LD changes, and the offset amount of the focus error signal deviates from the optimum value. SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has an optical disc capable of correcting a change in an offset amount of a focus error signal due to a change in light emission power and always setting an optimal focus error signal offset (hereinafter, focus offset) amount. and to provide a focus offset setting method for the drive.

[0004]

According to a first aspect of the present invention, there is provided a method for setting a focus offset of an optical disk drive, comprising: a focus error signal offset adjusting unit; and a nonvolatile memory. The tilt offset data and intercept data of the focus offset calculation primary straight line, which are offset adjustment data, were stored in the non-volatile memory, and the focus offset set value for the emission power of the laser diode during data writing was stored in the non-volatile memory. It is characterized by being calculated using data. According to a second aspect of the present invention, in addition to the first aspect, the focus offset setting method for an optical disk drive further comprises a temperature sensor for detecting an ambient temperature of the laser diode, and the non-volatile memory stores focus offset correction data for the ambient temperature of the laser diode. Is stored, and the focus offset set value is corrected based on the temperature detected by the temperature sensor. A focus offset setting method for an optical disk drive according to claim 3, comprising: a focus error signal offset adjusting unit; and a nonvolatile memory, and measuring a focus offset value with respect to emission power of at least two or more different laser diodes. From the measured values, an approximate expression representing the relationship between the focus offset value and the emission power is obtained, the coefficient used for the approximate expression is stored in the nonvolatile memory, and the focus offset setting value for the emission power of the laser diode at the time of data writing. Is calculated using data stored in the nonvolatile memory.

[0005]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of an optical disk drive according to the present invention will be described below with reference to FIGS. Figure 1 is a diagram showing the configuration of an optical disc drive according to the present invention, 1 controls the optical disk drive CP
U, 2 a non-volatile memory, 3 a D / A converter, 4 a signal processor, 5 an automatic gain controller (AGC), 6 an adder, 7 a digital signal processor (DSP), 8 a focus motor driver, 9 denotes an optical system unit (P / U). The optical system unit 9 includes an LD for irradiating a recording medium such as an optical disk with laser light, an objective lens for condensing the laser light on a recording / reproducing layer of the recording medium, and a light receiving element for converting reflected light from the recording medium into an electric signal. And the like, and a focus motor for moving the objective lens toward the recording medium. The CPU 1, the D / A converter 3, and the adder 6 function as a focus error signal offset adjusting unit. Next, the operation of the optical disk drive will be described. First, the CPU 1 takes out data for focus offset adjustment from the memory 2 immediately before writing to the recording medium, and calculates a focus offset value based on the light emission power of the LD at the time of writing. For example,
CD-R / writing speed in an optical disk such as RW (1
Fold, 2-fold, 4-fold, since the light emitting power of LD in accordance with the 8-fold.. Etc.) different, the focus offset value is calculated accordingly.

FIG. 2 shows an example of calculation of the focus offset value. The horizontal axis represents the light emission power of the LD, and the vertical axis represents the focus offset value. Assuming that the inclination of the primary line for focus offset calculation is A and the intercept is B, the focus offset value can be calculated by the following calculation. Focus offset value = emission power + B The focus offset value at the time of A × write is calculated by CPU 1, D
The signal is converted into an analog value via the / A converter 3 and supplied to the adder 6. The output of the adder 6 is supplied to a digital signal processing unit 7, which converts the input signal from analog to digital. Digital signal processing unit 7
Supplies a control signal to the driver 8 via a digital filter, and further, the driver 8 supplies a current to the focus motor. Further, a control signal is output from the CPU 1 so that the LD of the optical system unit 9 emits light at a desired light emission power, and the recording medium is irradiated with laser light. Therefore, the light reflected from the recording medium is received by the light receiving element of the optical system unit 9, and the received light output is supplied from the optical system unit 9 to the signal processing unit 4. The signal processing unit 4 generates a focus error signal according to the input light receiving level and supplies the focus error signal to the AGC 5. In the AGC 5, the gain is controlled so that the sensitivity of the focus error signal is kept constant with respect to the fluctuation of the reflected light from the recording medium. The output of the AGC 5 is supplied to the adder 6, where the focus offset value corresponding to the above-described light emission power and the focus error signal corresponding to the output of the light receiving element of the optical system unit 9 are added, and the digital signal processing unit 8 supplies the driver 8.
Is supplied with a control signal to drive the focus motor. For example, in an optical disc such as a CD-R / RW or the like in which a writing speed of 1, 2, 4, or 8 times can be set, the light emission power of the LD at the time of data writing increases in accordance with the writing speed. A large light emission power is required, and it is generally said that the light emission power becomes a root multiple of the writing speed. Therefore, there is a problem that the temperature of the LD changes due to the difference in the light emission power at the time of writing, and if the focus offset is constant, optimum writing control cannot be performed. Therefore, like the optical disk drive according to the present invention, data for adjusting a focus error offset is obtained from the memory 2 in accordance with the emission power, a focus offset value is calculated based on the obtained data, and the focus motor is controlled based on the calculated focus offset value. By driving, writing quality can be improved without generating a focus offset at the time of writing.

FIG. 3 is a diagram showing the relationship between the light emission power and the focus offset value at the time of writing. As described above, the writing speed is assumed to be 1, 2, 4, 8 times.
The relationship between the respective light emission powers and the focus offset is shown. Data is stored in the memory 2 so that the focus offset value indicated by the dashed line in the figure is obtained, and the CPU 1 sets the data. FIG. 4 is a diagram showing another embodiment of the optical disk drive according to the present invention. The same components as those in FIG. 1 are denoted by the same reference numerals, and description thereof will be omitted. The difference from the first embodiment is that a temperature sensor 10 for measuring the LD ambient temperature of the optical system unit 9 is provided, the output of the temperature sensor is converted into a digital signal via an A / D converter 11, and the digital signal is converted. The point is that the temperature information is supplied to the CPU 1. The memory 2 stores focus error offset adjustment data for the light emission power of the LD as in the first embodiment, and a correction coefficient A for the ambient temperature of the LD.
s, stores the Bs. FIG. 5 is a diagram showing the relationship between the LD ambient temperature and the correction value, and shows the slope As of the correction characteristic linear line.
And the intercept Bs are stored in the memory 2 to obtain the LD ambient temperature information.
It is possible to calculate the correction value by using the s. That is, as described in the first embodiment, the CPU 1 calculates the focus offset value based on the light emission power of the LD, obtains the correction coefficients As and Bs based on the LD ambient temperature information from the temperature sensor 10, and performs the write operation. , And an optimum focus offset can be set from the focus offset value and the focus offset correction value.

FIG. 6 is a diagram showing a focus offset in which a focus offset correction value is further added to the relationship between the light emission power and the focus offset value at the time of writing shown in FIG. 3, and a broken line indicates only the light emission power of the LD at the time of writing. The dashed line indicates the focus offset obtained by adding the focus offset correction value based on the LD ambient temperature to the focus offset based on the light emission power of the LD at the time of writing. Since the focus offset correction value changes due to a change in the ambient temperature, the focus offset value that takes the ambient temperature of the LD into consideration cannot always be represented by a single straight line. Is simply indicated by a dashed line. That is, the dashed line is a focus offset value using the focus offset calculation coefficients A and B as the LD emission power at the time of writing, and the CPU 1 calculates this focus offset value, and further adds the correction coefficient As based on the ambient temperature to this focus offset value. And a correction value based on Bs is added to obtain a focus offset value indicated by a dashed line, and a control signal for driving a focus motor is output to the driver 8. Therefore, in the second embodiment, L
Since the focus offset is determined using the focus offset correction value based on the LD ambient temperature information from the temperature sensor 10 in addition to the focus offset value based on the light emission power of D, the focus offset during data writing does not occur. Writing quality can be improved.

In the first and second embodiments, the calculation of the focus offset value based on the light emission power of the LD at the time of data writing and the calculation of the focus offset correction value based on the LD ambient temperature are performed on the assumption of a primary straight line. However, the relationship between the LD power and the focus offset value may not be proportional to a linear function due to variations in the characteristics of each LD and the heat radiation state of the LD. Therefore, as shown in FIG. 7, the focus offset value with respect to the LD emission power at the time of data writing is measured in advance, an approximate expression is obtained from the measured value, the coefficient is stored in the memory 2, and the focus offset value is calculated. Good. Curve 1 in the figure is the relationship between the LD emission power and the focus offset measurement value when the optical disc drive M, curve 2 shows the relationship between the LD emission power and the focus offset measurement value when the optical disc drive N. As described above, in calculating the focus offset value in the optical disc drive M,
By obtaining the second order approximation formula and using the coefficients (Cm, Am, Bm) and storing them in the memory 2 so that the optical disc drive N uses (Cn, An, Bn) as the second approximation formula coefficient. can be variations among improves the writing quality eliminated. The focus offset value calculated by the second-order approximation equation used to set a value that depends on the emission power of the LD, and further described LD
The correction based on the ambient temperature may be used together.

[0010]

As described above, according to the first aspect of the present invention, although the light emission power of the LD changes depending on the data writing speed, the offset value of the focus error signal is set to L.
Since the adjustment can be made optimally according to the light emission power of D, the data writing quality can be improved. The second aspect of the present invention described the effect of the invention according to claim 1, wherein,
Since the offset value of the focus error signal can be optimally adjusted according to the light emission power of the LD and the ambient temperature of the LD, the data writing quality can be further improved. In the invention according to claim 3, the light emission power and the focus offset amount at the time of LD writing are measured in advance for each optical disk drive, and an approximate expression is obtained from the measured values.
The coefficient that satisfies the approximation formula is stored in the memory, and the focus offset value is calculated using the approximation formula from the light emission power at the time of writing, so that the focus offset value is optimally adjusted without being affected by the variation of each optical disc drive, Data writing quality can be improved.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of an optical disk drive according to the present invention.

FIG. 2 is a diagram showing a calculation example of a focus offset value.

FIG. 3 is a diagram showing a relationship between light emission power and a focus offset value at the time of writing.

FIG. 4 is a diagram showing another embodiment of the optical disk drive according to the present invention.

Figure 5 is a graph showing a relation of the LD ambient temperature and a correction value.

FIG. 6 is a diagram showing a focus offset taking into account a focus offset correction value.

FIG. 7 is a diagram for explaining an approximate expression of a focus offset value with respect to LD emission power.

[Explanation of symbols]

1 ... CPU, 2 ... Non-volatile memory,
3 ... D / A conversion unit, 4 ... signal processing unit, 5 ...
..Automatic gain control section (AGC), 6 ... adder,
7 ... Digital signal processing unit (DSP), 8 ... Focus motor driver, 9 ... Optical system unit (P / U), 10 ... Temperature sensor, 11 ...
A / D converter

Claims (3)

[Claims] An offset adjustment unit for a focus error signal; and a nonvolatile memory, wherein inclination data and intercept data of a primary line for focus offset calculation as focus offset adjustment data are stored in the nonvolatile memory, A focus offset setting method for an optical disk drive, wherein a focus offset set value for a light emitting power of a laser diode at the time of data writing is calculated using data stored in the nonvolatile memory. 2. A temperature sensor for detecting an ambient temperature of a laser diode, a focus offset correction data for the ambient temperature of the laser diode is stored in the non-volatile memory, and a focus offset set value is determined by a temperature detected by the temperature sensor. 2. The focus offset setting method for an optical disk drive according to claim 1, wherein the correction is performed. 3. A focus error signal offset adjusting means and a non-volatile memory, wherein a focus offset value with respect to emission power of at least two or more different laser diodes is measured, and a focus offset value and light emission are measured from the measured values. Data obtained by obtaining an approximate expression representing a relationship with power, storing a coefficient used in the approximate expression in the non-volatile memory, and storing a focus offset setting value for a light emitting power of a laser diode at the time of data writing in the non-volatile memory. A focus offset setting method for an optical disc drive, wherein the focus offset setting method calculates the focus offset using an optical disk drive.