JPS63281230A - Focus servo device for optical pick-up - Google Patents

Abstract

PURPOSE:To obtain a focus servo action with a high stability by operating a servo loop at the time of exceeding a second level after a focus error signal exceeds a first level. CONSTITUTION:A servo switch control part 5, at the time E when a focus error signal (f) exceeds a first signal level VH, comes to be enable, and at the time F of exceeding a second signal level VL, the servo switch is turned on. As the result, only when an objective lens is near a focus point position, a servo action is started. Thus, a malfunction due to the noise can be prevented, the behavior nonuniformity of the focus error signal due to variance in the optical type, etc., occurs and even then, the servo action is stably started at a prescribed action point.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a focus servo Bffff of an optical pickup used in an optical memory or the like, and more particularly to a focus servo device that is less susceptible to noise and has high stability.

(Background of the Invention) For example, an optical memory is configured to optically read out bits recorded on an optical disk using an optical pickup.

In order to stably read the bits recorded on the optical disk in such an optical memory, the optical pickup must be moved so that the optical beam of the optical pickup follows a single spiral bit track formed on the optical disk. In addition to moving the optical pickup in the horizontal direction, the entire optical pickup or only the objective lens constituting the optical pickup is moved in accordance with the vertical movement of the optical disk so that the distance between the objective lens constituting the optical pickup and the recording surface of the optical disk is always kept constant. It needs to be moved up and down.

Therefore, a track servo mechanism is used to make the optical pickup follow the bit track of the optical disk, and a focus servo mechanism is used to keep the distance between the objective lens that makes up the optical pickup and the recording surface of the optical disk constant. .

By the way, in general, in a focus servo mechanism, a focus error signal is obtained by the astigmatism method, Foucault method, +m field angle method, etc., and a servo loop is operated so that the focus error signal becomes zero. . and,
To start such a servo loop operation, the objective lens is gradually brought closer to the recording surface of the optical disk, and when it is detected that the focus error signal crosses zero,
When the switch for operating the servo loop is turned on or when it is detected that the focus error signal becomes zero while the level of the tracking error signal is high as shown in Japanese Patent Application Laid-Open No. 61-61238. , turning on the switch to operate the servo loop is done.

(Problems to be Solved by the Invention) However, the former configuration that simply detects the zero of the focus error signal has a problem in that it easily malfunctions due to noise being superimposed on the focus error signal. Malfunctions may also occur due to variations in the mounting accuracy of the optical system.

For example, when a current is applied to the objective lens drive coil and the objective lens is brought close to the recording surface of the optical disk, the detector outputs a focus error signal as shown in FIG. 8. A and B in the figure.

Zero cross detection is performed at each point C and D, but at point A.

B and C are defocus positions where the objective lens has not yet reached the in-focus position, that is, it is out of focus, and D is the in-focus position where the objective lens has reached the in-focus position. A, B, C
is the zero cross point caused by the noise, etc., so
The servo loop must be activated at point D, and A, B
, C, the objective lens will stop at the defocused position, making it impossible to stably detect the bits on the optical disc.

On the other hand, in order to detect the zero cross of the focus error signal when the level of the tracking error signal is high as in the model configuration, an envelope generation circuit and a waveform shaping circuit for the tracking error signal are required. It gets complicated. or,
If the frequency component of the tracking error signal fluctuates, the envelope generating circuit will not operate properly, resulting in unstable servo operation.

The present invention has been made in view of the above-mentioned problems.The purpose of the present invention is to provide a focus servo for an optical pickup that has a relatively simple circuit configuration and is less susceptible to noise and variations in the mounting accuracy of the optical system. The purpose is to realize the device.

(Means for Solving the Problems) The present invention, which solves the above-mentioned problems, provides first and second levels that are different from the fluctuation range of the focus error signal outside the vicinity of the in-focus point and sandwich the fluctuation range. Means for setting VH and VL and comparing the levels with a focus error signal, and a servo switch that is set to be enabled when the focus error signal output from the optical big A2 tube exceeds the first level VH. 1 lilj m1 part and
and a servo switch that is turned on by the servo switch control section when the focus error signal fluctuates and exceeds the second level VL after the servo switch control section is set to enable. It is.

(Function) According to the focus servo device for a pickup according to the present invention, the servo loop is activated when the focus error signal exceeds the second level in a manner similar to when the focus error signal exceeds the first level.

Therefore, the servo loop always operates near the in-focus position, and a highly stable focus servo operation can be obtained.

(Embodiments) Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a block diagram showing one embodiment of the present invention. In FIG. 1, 1 is an input terminal to which a focus error signal f is applied, which is connected to a high level discriminator 2 and a low level discriminator 3, and is also connected to an input terminal of a servo switch 4 that controls the operation of the servo loop. It is connected. 5
is a servo switch control section, which uses the detection signal a of the high level discriminator 2 as an enable signal, and uses the detection signal a of the high level discriminator 2 as an enable signal, and the low level discriminator 3
Using the detection signal C as a clock, the control signal C for turning on and off the servo switch 4 is sent to the servo switch 4.
Output to. The output signal g of the servo switch 4 takes the value of the focus error signal f or high impedance depending on the level of the control unit @C applied from the servo switch control unit 5. The output signal Q of the servo switch 4 is input to a servo amplifier.

FIG. 2 is a timing chart for explaining the operation of FIG. 1. The detection signal a of the high level discriminator 2 rises from the L level to 1 level when the focus error signal f reaches a value higher than the first level VH (VH is outside the fluctuation range due to noise, etc.), and the servo switch control is performed. 5 is set to an enabled state. The detection signal of the low level discriminator 3 is normally set to the L level, and becomes the H level only during the period when the focus error signal f is lower than the second level VL (VL is outside the fluctuation range due to noise etc.). Become. The control unit @C of the servo switch control unit 5 is configured such that the detection signal @b of the low level discrimination unit 3 is L in the enabled state.
The output signal 9 of the servo switch 4 is in high impedance while the control signal C applied from the servo switch control section 5 is at the L level. , when the control signal C rises to 1 level, it takes on the value of the focus error signal t.

The servo loop starts servo operation when the output signal of the servo switch 4 applied to the servo amplifier changes from high impedance to the focus error signal f.

FIG. 3 is a circuit diagram showing a specific example of FIG. 1, and the same parts as in FIG. 1 are given the same reference numerals. In Figure 3,
The high level discrimination section 2 includes a comparator 6 and a D-type flip 7.
The low level discrimination section 3 is composed of a comparator, the servo switch 4 is composed of an analog switch, and the servo switch control section 5 is composed of a D-type flip-flop 7.

FIG. 4 is a diagram showing an example of the overall configuration including the circuit of the present invention, and the same parts as in FIG. 1 are given the same reference numerals. In FIG. 4, the blocks surrounded by broken lines correspond to the circuit of the present invention. The focus error signal f is applied to the servo amplifier 8 via the circuit of the present invention. The servo amplifier 8 drives an actuator via a driver 9 to move the optical pickup in a direction where the focus error signal r becomes zero.

As a result, the distance between the optical pickup and the recording surface of the optical disc is always kept in focus.

FIG. 5 is an explanatory diagram of such an operation, and shows the focus error signal @f similar to FIGS.

That is, the servo switch control section 5 receives the focus error signal f.
The servo switch is enabled at a time point E when the signal level exceeds the first signal level VH, and turns on the servo switch at a time point F when the signal level exceeds the second signal level VL. As a result, the servo operation is started only when the objective lens is near the in-focus position.

With this configuration, it is possible to prevent malfunctions caused by noise as in the conventional case. Further, even if non-uniform behavior of the focus error signal occurs due to variations in the optical system, etc., the servo operation will stably start at a predetermined operating point. Furthermore, such a circuit can be constructed relatively easily.

The servo switch 4 may be connected to selectively ground the input terminal of the servo amplifier 8 as shown in FIG. 6, or may be connected to ground the input terminal of the servo amplifier 8 as shown in FIG. The drive signal may be connected to be selectively turned on or off.

Further, the servo switch 4 may be a mechanical relay switch or the like.

Further, in place of the D-type flip-flop 5.7 in FIG. 3, part of the functions of a microprocessor used in an optical disk drive may be used.

Further, the levels vH and vL are set assuming a focus error signal t as shown in FIG. 5, and if the polarity of the focus error signal is reversed, VL>VH. In addition, V
H and VL may be outside the range of variation of the focus error signal outside the vicinity of the in-focus point (one is greater than the upper limit and the other is less than the lower limit), but must be within the maximum amplitude of the focus error signal.

(Effects of the Invention) As described above, the present invention provides a focus servo device for an optical pickup that has a relatively simple circuit configuration and is less susceptible to noise and variations in mounting accuracy of the optical system and has high stability. realizable.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a timing chart for explaining the operation of FIG. 1, FIG. 3 is a circuit diagram showing the shell example of FIG. 1, and FIG. The figure is an example of the overall configuration including the circuit of the present invention, FIGS. 5 and 6 are other examples of the overall configuration, FIG. 7 is a signal waveform diagram for explaining the present invention in detail, and FIG. 8 is the conventional circuit. FIG. 3 is a signal waveform diagram for explaining the operation. DESCRIPTION OF SYMBOLS 1... Focus error signal input terminal 2... High level discrimination part 3... Low level discrimination part 4... Servo switch 5... Bo-bo switch control part 8... Servo amplifier 9... Driver patent applicant Roku Konishi Photo Industry Co., Ltd. Agent
Patent attorney Fuji Ijima 1 person outside the jurisdiction - Taku 5 Figure R Seimachi Figure 6 Figure 7 Corner ■ Figure 8

Claims (1)

[Claims] means for setting different first and second levels V_H and V_L so as to sandwich the variation range outside the variation range of the focus error signal outside the vicinity of the in-focus point, and comparing the levels with the focus error signal; The focus error signal output from the pickup is at the first level V_H.
a servo switch control section that is enabled when the servo switch control section exceeds the second level V_L; A focus servo device for an optical pickup, comprising a servo switch.