JPH10255283A - Method for controlling optical pickup and optical disk apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a control method for an optical pickup which maintains a stable servo state, is suitable to make the optical pickup compact and light- weight and widen a servo band independently of the temperature of an environment where the optical pickup is used. SOLUTION: An IC 9 having a temperature detector is added, and a gain of a DSP 13 is adjusted by a CPU 15 at all times so as to constitute an optimum servo system on the basis of a temperature detection output from the IC 9. A control system is constituted of an RF.AMP 12 extracting a tracking error and a focus error from a detection signal of an optical pickup 11, the DSP 13 determining a controlled variable on the basis of error signals, a driving circuit 14 receiving the controlled variable from the DSP 13 and controlling the position of a lens of the optical pickup 11, the IC 9 detecting the temperature of an environment where the optical pickup is used, and the CPU 15 operating an optimum servo gain on the basis of the temperature detection output of the IC 9.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for controlling an optical pickup in which tracking servo and focus servo are performed under optimum conditions irrespective of a use environment temperature, and an optical disk apparatus using the control method.

[0002]

2. Description of the Related Art With the recent development of the information-oriented society, it has been required to store a large amount of information and process it at high speed. As a result, optical disk recording media have become extremely popular as means for storing large amounts of data, and CDs, MDs, DVDs
From playback-only types to types that can record and play back,
Various things have been proposed and commercialized.
At the same time, further improvement in performance of the recording / reproducing control system for these optical disks has been demanded.

Next, a configuration of a control system including an optical pickup and a control form thereof will be described with reference to FIGS. FIG. 4 is a plan view of the optical pickup, and FIG.
6 is an equivalent model of the vibration system of the optical pickup, and FIG. 6 is a diagram showing the transfer characteristics of the optical pickup shown in FIG.
FIG. 7 is a diagram showing the relationship between the temperature and the gain of the optical pickup, and FIG. 8 is a diagram showing the loop characteristics of the servo system.

As shown in FIG. 4, one example of an optical pickup is provided on an optical pickup housing 1 with two main shaft fulcrums 2 for moving in the radial direction of an optical disk, and one provided on a side opposite to the main shaft fulcrum 2. Two auxiliary shaft fulcrums 3, a laser 4 as a light source, an optical sensor 5 for detecting reflected light from the optical disk, a lens 6 for condensing the laser light from the laser 4 on the optical disk, other optical components, and position control of the lens 6 A tracking drive mechanism and a focus drive mechanism are provided. Many of these components are covered by a cover 7 to prevent dust and the like from the outside. Further, the optical pickup and the external mechanism exchange electric signals via the flexible plate 8.

First, a vibration model of a general optical pickup will be described. As shown in FIG. 5, all masses whose position is controlled, such as a lens of an optical pickup, are represented by M [Kg],
The compliance of the spring is C [m / N], the reciprocal of the viscous resistance of the vibrating part is R [m / N · sec], and the driving force is F
[N], displacement is L [m], and angular frequency is ω [rad / se
c], transfer function G (jω) = displacement / driving force [L
/ F] is

(Equation 1) It can be expressed as. Therefore, the gain | G (jω) |

(Equation 2) And the phase ∠G (jω) is

(Equation 3) Becomes

When the gain and phase of the transfer function G (jω) are plotted on the horizontal axis with the angular frequency ω as shown in FIG. 6, the resonance point ω ₀ becomes

(Equation 4) Becomes At this angular frequency ω ₀ , the gain has a peak, and at an angular frequency lower than ω ₀ , the gain is constant.
_At angular frequencies higher than ₀ , the frequency is attenuated at -12 dB / oct. Also, the phase starts at 0 degree and 90 at ω ₀
The degree lag converges to a 180 degree lag as it becomes higher than ω ₀ .

However, this characteristic is obtained when an ideal vibration model is considered. In practice, a dip occurs on the transfer function G (jω) due to insufficient strength of components, structure, optical factors, etc. _{In a} band slightly higher than ₀ , the phase may be delayed by 180 degrees or more. Usually, in consideration of this point, the DSP (Digital Signal) of the servo system is used.
1 Processor). In addition, as shown in FIG. 4, when a three-point support structure is used to reduce the size and weight, or in particular, the auxiliary shaft fulcrum 3 cannot be set at the center of the side, and the center of gravity of the optical pickup is set to the two main shaft fulcrums 2. It is also known that the control of the optical pickup is made more unstable even when it cannot be arranged inside the triangle constituted by the counter shaft fulcrum 3.

Now, for a control system using an optical pickup basically composed of the above-described system, the gain of the servo system was measured using the operating environment temperature as a parameter.
As shown in FIG. 7, an increase in gain was observed as the temperature decreased, and it was observed that this increase caused oscillation in the servo system. It is thought that the cause of this gain increase is inherent in the optical pickup, and the inherent characteristics of the supporting structure and material of the movable portion, the laser and other optical components change due to a decrease in temperature, and these factors are considered to occur in combination. I have.

Next, the temperature decreases and the gain increases,
The mechanism by which the servo system oscillates will be described with reference to FIG. | G | ₁ in FIG. 8 is a loop gain at the reference operating temperature T ₁ . In this example, the loop gain is set to 0 dB at f ₁ at the temperature T ₁ , and the phase margin at f ₁ is sufficiently large at θm ₁ . Also, the phase ΔG
Is −180 ° at f ₃ , and the gain margin at this time is g
and take a sufficient margin in m _1. Therefore, this servo system is in a stable state and has a servo band of 1 KHz if f ₁ , that is, if f ₁ = 1 KHz.

The temperature of | G | ₂ is T ₂ (T ₁ >
T ₂ ), where Δ | G | = | G
This indicates that the gain has increased by | ₁₋ | G | ₂ . As described above, this rise is mainly caused by the optical pickup, and it is generally recognized that Δ | G | rises by 3 to 5 dB. If the gain becomes 0 dB at f ₂ (f ₁ <f ₂ ) at the temperature T ₂ , the phase margin θm ₁ changes to θm ₂ (θm ₂ <θm ₁ ) in this state, and the temperature T ₁
The servo system becomes more unstable than in the case of. In particular, as the operating temperature decreases, the loop gain increases, so that the phase margin decreases, the servo system tends to become unstable, and oscillation easily occurs at a dip point or the like. Note that the phase ΔG is substantially constant regardless of the temperature.

As described above, it can be seen that when the use environment temperature decreases, the loop gain of the servo system increases, the servo system becomes unstable, the optical pickup resonates, and information recording / reproduction on the optical disk cannot be performed. As a countermeasure against this, measures such as increasing the mechanical strength of the optical pickup and reinforcing a portion that easily resonates have been adopted. However, these methods are contrary to the miniaturization and weight reduction of the optical pickup, the widening of the bandwidth of the servo, and the increase in cost.

[0012]

Accordingly, the present invention is suitable for miniaturization, weight reduction, and broadening of the servo band without oscillating the servo system even when the use environment temperature is lowered in information recording / reproducing of the optical disk. It is an object of the present invention to provide a method for controlling an optical pickup and an optical disk device using the control method.

[0013]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and provides a temperature detector in a control system including an optical pickup used for recording and reproduction of an optical recording medium. An optical pickup control method for determining a tracking servo loop gain and a focus servo loop gain of the control system based on a detection output of a detector, and an optical disk apparatus using the control method are provided to solve the above-described problems.

The servo loop characteristic including the optical pickup and the control circuit can be stabilized by always setting the optimum servo loop gain at that temperature by, for example, a CPU based on the detection output of the temperature detector. Therefore, it is possible to prevent the optical pickup from resonating at a wide use environment temperature.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a block diagram showing a servo configuration of the present invention, FIG. 2 is a diagram showing transfer characteristics by a DSP and a drive circuit, and FIG. 3 is a flowchart showing an example of a servo flow of the present invention. .

FIG. 4 shows an optical pickup used in the present invention.
And the detailed description thereof is omitted.

As shown in the block diagram of FIG. 1, the servo system includes an RF AMP 12 for extracting a tracking error and a focus error from a detection signal of the optical pickup 11,
DSP 13, which determines the control amount based on the error signal,
A drive circuit 14 for controlling the position of the lens of the optical pickup 11 to which a control amount is input from the DSP 13, an IC 9 including a temperature detector for detecting a use environment temperature, and an optimum servo loop gain based on a temperature detection output of the IC 9 And a CPU 15 that computes

The operation of the servo system will be described.
CPU 15 calculates the correction amount of the servo loop gain based on the temperature detection output, and acts on DSP 13. That is, the transfer characteristic of the DSP and the drive circuit is determined as shown in FIG. 2, and the transfer function and the transfer function of the optical pickup shown in FIG. Then, the optical pickup 11 is controlled. Here, the loop gain is determined so as to reduce the gain increase Δ | G | at the temperature T ₂ (T ₁ > T ₂ ) in the use environment from the reference temperature T ₁ to provide a stable servo system. . Therefore, the present invention can provide the optical pickup 11 to an optical disk device without causing resonance at a wide use environment temperature.

Next, an example of the flow of control by the CPU 15 will be described with reference to FIG.

First, a temperature is measured at the start of use of the optical disk device (step 101). Next, the tracking gain and the focus gain of the DSP 13 at the use start temperature are initialized (Step 102). Thereafter, the servo is started (Step 103), and after a predetermined time has elapsed (Step 104), the temperature is measured (Step 105), and the tracking gain and focus gain of the DSP 13 corresponding to the temperature are newly set (Step 106). ).
Next, it is determined whether or not to continue use (step 10).
7) To continue, return to step 104, and from step 104 to step 106,
Keep setting the tracking gain and focus gain of.

[0021] The present invention when lowered from the reference temperature T ₁ of have been described for, it will be appreciated that it is possible to maintain optimal servo system in the same manner also when becomes higher from the reference temperatures T _1. That is, when the temperature rises, the loop gain decreases and the servo band becomes narrower.
The optimum servo system can be maintained by increasing the gain of the DSP 13 by reducing the loop gain by the U15.

Further, by using the above-described optical pickup control method, it is possible to configure an optical disk device that is small, lightweight, and has a wide servo band.

The temperature detector may be set at any location as long as the temperature is substantially the same as the operating environment temperature of the optical pickup. Further, the present invention is not limited to the block configuration and the flow of the control processing described in the embodiment, and it is obvious that various methods for embodying the technical idea of the present invention can be adopted.

[0024]

As is apparent from the above description, according to the present invention, the optimum servo system at the operating environment temperature can always be set based on the detection output of the temperature detector. It is possible to provide a control method of an optical pickup suitable for miniaturization, weight reduction, and widening of a servo band, and an optical disk apparatus with high performance using this control method, without depending on the control method.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a servo configuration of the present invention.

FIG. 2 is a diagram illustrating transmission characteristics of a DSP and a drive circuit.

FIG. 3 is a flowchart showing an example of a servo flow according to the present invention.

FIG. 4 is a plan view of the optical pickup.

FIG. 5 is a diagram showing an equivalent model of a vibration system of the optical pickup.

FIG. 6 is a diagram illustrating transfer characteristics of the optical pickup illustrated in FIG. 5;

FIG. 7 is a diagram illustrating a relationship between temperature and gain of the optical pickup.

FIG. 8 is a diagram illustrating a loop characteristic of a servo system.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Optical pickup housing, 2 ... Main shaft fulcrum, 3 ... Sub shaft fulcrum, 4 ... Laser, 5 ... Optical sensor, 6 ... Lens, 7 ... Cover, 8 ... Flexible board, 9 ... IC, 11 ... Optical pickup,
12 RF / AMP, 13 DSP, 14 drive circuit,
15 ... CPU

Claims (2)

[Claims] A temperature detector is provided in a control system including an optical pickup used for recording and reproduction of an optical recording medium, and a tracking servo loop gain of the control system is determined based on a detection output of the temperature detector. And a focus servo loop gain. 2. An optical disk device using the method for controlling an optical pickup according to claim 1.