JP2523866Y2 - Focus servo retractor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a focus servo retracting device, and more particularly to a focus servo retracting device that enables stable servo system retracting.

(Prior Art) For example, in a CD player, a compact disk is irradiated with laser light from a pickup through a lens, and light reflected from the disk surface is received by a light receiving element to read information on a disk surface storage medium. I have. At this time, the pickup is vertically moved using a servo mechanism so that the disk surface is positioned (focused) at the focal position of the lens.

Conventionally, in such focus servo control, since the area where the servo error signal can be detected is narrow, the servo loop is first turned off and the focus actuator is moved up and down to enter the above area and focus servo control is started. Let me.

FIG. 3 shows a configuration block diagram of a conventional focus servo pull-in device.

The focus error signal FE is supplied from the focus error detection circuit 1 to the switch SW1 and one input terminal (+ terminal) of the comparator 6. The variable resistor VR1 is for compensating a factor of asymmetry caused by a variation in sensitivity between divided detection areas of the photodetector in the astigmatism method, and is called FE balance adjustment.

The compensation circuit 2 is a circuit that corrects the frequency characteristics and phase of the focus error signal in order to perform stable servo control, and has a function that operates only when the switch SW1 is closed.

The focus search voltage generation circuit 5 generates a voltage signal for moving the pickup to an area near the focal point as described above. The switch SW2 is closed before the operation of the focus servo system, and is opened when the operation of the focus servo system is started.

A voltage level (reference level signal) V _REF divided by the resistors R ₁ and R ₂ is supplied to the other input terminal (−terminal) of the comparator 6, and a focus error signal from the focus error detection circuit 1 is supplied. The FE is compared with the reference level signal, and an FZC (Focus Zero Comparator) signal is sent to the switch control circuit 7 when the FE is equal to or higher than the reference level signal. Here, the reference level signal V _REF removes the influence of the noise level.

The switch control circuit 7 opens the switch SW1 and closes the switch SW2 at the initial stage before the start of the operation of the focus servo system, and when the FZC signal is received, closes the switch SW1 and opens the switch SW2. Then, a focus servo operation and a focus servo pull-in operation are performed.

FIG. 4 is a timing chart illustrating the configuration operation of FIG. When the S-type focus error signal FE has exceeded the reference level signal V _REF , the comparator 6 outputs the FZC signal shown in FIG.
The switch SW1 and the switch SW2 are controlled through the switch. A signal is supplied to the driver 3 via the switches SW1 and SW2 to the focus actuator coil 4 to move the pickup.

(Problem to be Solved by the Invention) As described above, in the conventional focus servo pull-in device, the reference level signal V _REF and the focus error signal FE
The switches SW1 and SW2 are controlled based on the result of the comparison.

However, the focus error signal FE does not have a clean waveform, but has a swell as shown in FIG. 4. To avoid this, the reference level signal V
I had a _REF . However, since noise components overlap as shown in the enlarged view 41, chattering occurs in the comparison result FZC signal, and a chattering prevention circuit must be added separately. Further, since the comparison level is not O _v, the focus servo pull-in point is not focused,
It is shifted by the reference level signal V _REF . Therefore,
There has been a problem that the stability of the operation of the retractable character of the servo system is impaired.

Therefore, an object of the present invention is to provide a focus servo pull-in device in which the stability of the operation of the focus servo system is greatly improved.

(Means for Solving the Problems) In order to solve the above-mentioned problems, a focus servo pull-in device according to the present invention compares a focus error signal level with a predetermined reference level using a comparator, and performs focus servo control according to the comparison result. A focus servo pull-in device for performing pull-in, wherein the focus error signal is supplied to one end, and a voltage dividing circuit that divides the focus error signal level and inputs a divided voltage to the comparator; Is connected to the other end of the voltage dividing circuit.

(Operation) In the present invention, the voltage dividing circuit adds an offset to the focus error signal so as to cancel the reference level after the comparison and detection. That is, an error is prevented from occurring by applying the same voltage as the reference level to the focus error signal at the focal point.

(Example) Next, this invention is demonstrated, referring drawings.

FIG. 1 is a block diagram showing an embodiment of a focus servo pull-in device according to the present invention. In FIG. 1, the components denoted by the same reference numerals as those in FIG.
It shows the same components as in the figure.

In the present invention, the signal supplied to one input terminal of the comparator 6 is changed to the FE signal from the focus error detection circuit 1 by a resistor kR
While the divided partial pressure voltages V _{1 2} and kR ₁ and connects the output of the comparator 6 to the other end of the resistor kR ₁ through the capacitor C _1. Here, the resistors kR ₁ and kR ₂ and the capacitor C ₁
Constitute a voltage divider circuit 8, the capacitor C ₁ is provided for blocking the DC component.

First, the switch SW1 is controlled by the switch control circuit 7.
Is opened and SW2 is closed, the focus search voltage is sent from the focus servo voltage generation circuit 5 to the driver 3, and the pickup is brought closer to the disk. A focus point exists while the pickup is approaching the disk. At this time, the focus error detection circuit 1 outputs the FE signal shown in FIG.
An S-shaped waveform such as a signal is obtained and sent to the voltage dividing circuit 8. Here, if the time constant of kC ₁ (R ₁ + R ₂ ) is made sufficiently large with respect to the frequency of the FE signal, C ₁ can be ignored.

Rise in the the FE waveform signal _{FE, R 1 / (R 1 +} R 2), pressurized binary becomes V ₁ and. When V ₁ is greater than the reference level signal V _REF, the output is "HIGH" next to the comparator 6, the output voltage at this time is V _cc.

At this time, V ₁ is given by V ₁ = (R ₂ · V _cc + R ₁ · FE) / (R ₁ + R ₂ ) (1), and when FE is zero, that is, when the focal point is obtained, the expression (1) becomes _{1 = R2 · V cc / (} R 1 + R 2) ... a (2). This is the same voltage as V _REF . Therefore,
At the focal point, the FZC signal becomes “LOW”. Relationship between the signals V ₁ and the signal FE is shown in Figure 2.

The switch control circuit 7 closes the switch SW1, opens the switch SW2, closes the servo loop, applies the focus servo, and completes the pull-in.

In the above embodiment, the voltage dividing circuit is composed of a resistor. However, it goes without saying that another element such as a diode may be used.

(Effects of the Invention) As described above, in the present invention, the focus error signal is divided by the voltage dividing circuit and supplied to the comparator, and the noise component is superimposed on the focus error signal because of the hysteresis. In this case, an accurate focal point can be detected without malfunction, and stable focus servo can be performed.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of a focus servo pull-in device according to the present invention, FIG. 2 is a timing chart showing the operation of the configuration in FIG. 1, and FIG. 3 is a block diagram showing the configuration of a conventional focus servo pull-in device. FIG. 4 is an operation timing chart of the configuration of FIG. DESCRIPTION OF SYMBOLS 1 ... Focus error detection circuit, 2 ... Compensation circuit, 3 ... Driver, 4 ... Focus actuator coil, 5 ...
Focus search voltage generation circuit, 6 comparator, 7 switch control circuit, 8 voltage divider circuit.

Claims (1)

(57) [Scope of request for utility model registration] 1. A focus servo pull-in device for comparing a focus error signal level with a predetermined reference level by a comparator and performing a focus servo pull-in according to a result of the comparison. A focus servo pull-in, comprising a voltage dividing circuit for dividing an error signal level and inputting a divided voltage to the comparator, wherein the output of the comparator is connected to the other end of the voltage dividing circuit. apparatus.