JPH0237183Y2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION This invention relates to a recorded information reading device, and more particularly to a recorded information reading device having a servo system that controls the deviation of a recorded information detection point on a recording surface in accordance with a servo error signal.

FIG. 1 is a schematic block diagram of a tracking servo system in an optical recorded information reading device. A servo error signal from a tracking error signal generator 1 is sent to a drive amplifier 4 via an equalizer amplifier 2 and a servo loop switch 3. applied. The output of this drive amplifier becomes a drive signal for the tracking actuator 5, and the laser spot light, which is the recording information detection point, is biased and driven in a direction substantially perpendicular to the recording track. This tracking actuator 5 consists of a drive coil 51 and a tracking mirror 52, and the positional deviation of the spot light is controlled in accordance with the rotation angle of this mirror 52.

On the other hand, a resistor 6 is inserted in series with the coil 51 in order to detect the rotation angle of the tracking actuator.
The drive current flowing through the sensor is detected and converted into a voltage. This detection voltage is LPF (low pass filter) 7
, and only the low frequency components are extracted. this
A window comparator 8 detects whether the output of the LPF 7 is at a level within a predetermined range, and if it is outside this range, a detection output is generated and an MMV (monosubable multivibrator) 9 is triggered.
The loop switch 3 is controlled to open by the output of the MMV9.

Suppose now that a scan operation, which is one type of special playback, is performed. In this operation, the recording information detection point is rapidly forwarded in the direction perpendicular to the recording track while the tracking servo loop is turned on, and reproduction is performed. It is necessary to break the loop and return the mirror to its neutral rotational point. Therefore, this mirror rotation angle is detected by the LPF 7, and the vertical comparison level of the comparator 8 is selected to be smaller than the level corresponding to the mirror rotation limit, so that the servo is activated before the mirror 52 reaches the rotation limit. The loop is interrupted for a predetermined period of time.

During this loop break period, that is, during the existence of the output pulse of the MMV 9, the tracking mirror 52 returns to its rotational neutral point, and then the loop is turned on again and the above operation is repeated. Furthermore, since the servo locks stably when the relative speed between the recording track and the recorded information detection point at the moment of loop-on is small, the frequency of the servo error signal is monitored by the detector 10, and when the frequency becomes low, the MMV9 is detected.
This is to reset the .

FIG. 2A shows the output waveform of the LPF 7 during scan operation, and V _H is the upper reference level of the comparator 8.

If a tracking actuator 5 with a high Q frequency response characteristic is used, a hold circuit using a capacitor may be added after the loop switch 3 to control its damping. In such a case, the output waveform of the LPF 7 will be as shown in FIG. 2B.
In other words, depending on the relationship between the time constant of the LPF7 capacitor (power storage element), the time constant of the hold circuit, and the scan speed, as shown in Figure B.
The capacitor constituting the LPF 7 is charged before being discharged, and eventually reaches the reference level of the comparator 8 and no longer changes.

The present invention has been made to eliminate the drawbacks of such conventional devices, and is designed to control the discharge of the electric charge of the storage element constituting the LPF for detecting the rotation angle of the tracking actuator when the servo loop is disconnected. An object of the present invention is to provide a recorded information reading device that stabilizes the rotation of a tracking actuator.

The recorded information reading device according to the present invention includes a servo loop that controls the deviation of a recorded information detection point on the recording surface according to a servo error signal, and extracts the low-frequency component of the drive signal of the actuator that biases and drives this recorded information detection point. A recorded information reading device comprising: a low-pass filter that outputs a servo loop; It is characterized by having a discharging means for discharging the electric charge of the electricity storage element.

An embodiment of the present invention will be described below with reference to FIG. In the figure, parts equivalent to those in FIG. This capacitor 72
A discharge switch 11 is provided in parallel with this capacitor 72 to discharge the charge. This switch is controlled on and off by the output of the MMV 9, and is controlled on and off in a complementary manner to the loop switch 3.

Since the other configurations are the same as those shown in FIG. 1, their explanation will be omitted.

FIG. 4 shows the output waveform of the LPF 7 of the device shown in _FIG . The discharging switch 11 is turned on at the same time as turning off the servo loop and cutting off the servo loop. Therefore, the charge in the capacitor 72 is instantly discharged and reset to the initial state. When the low frequency detector 10 detects that the relative speed between the recording information detection point and the recording track has become small, the MMV 9 is reset and the servo loop is turned on, and at the same time the discharge switch 11 is turned off. . Since this operation is repeated, the capacitor 7
2 is always in a discharge state at the moment the servo loop is turned on, so stable scan operation is possible.

As described above, according to the present invention, since stable scanning operation is possible, the scanning speed can be increased. Another advantage is that the time required for the output voltage of the LPF, which indicates the rotation angle of the tracking actuator, to reach the reference level of the comparator is always constant.

Note that the configuration of the LPF is not limited to the example shown in the drawings, but may be other types, such as a second-order low-pass filter circuit. Further, although a low frequency detector is used to determine the timing when the servo loop is turned on, it goes without saying that other configurations may be used. Furthermore, it can be applied not only to tracking servo systems but also to tangential servo systems (in which the time axis of the reproduced signal is controlled by controlling the deviation of the recorded information detection point in the tangential direction of the recording track). , and is applicable not only to optical recorded information reading devices but also to other types, such as electrostatic devices.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a conventional tracking servo system, FIG. 2 is a diagram explaining the operation of the device shown in FIG. 1, FIG. 3 is a block diagram of an embodiment of the present invention, and FIG.
The figure is a diagram illustrating the operation of the apparatus shown in FIG. 3. Explanation of symbols of main parts, 1...Servo error signal generator, 3...Loop switch, 5...Tracking actuator, 7...LPF, 8...Window comparator, 9...MMV, 11... discharge switch.

Claims (1)

[Scope of utility model registration request] A servo loop that controls the deviation of a recorded information detection point on a recording surface in accordance with a servo error signal, a low-pass filter that extracts a low-frequency component of a drive signal of an actuator that bias-drives the recorded information detection point, and A recorded information reading device comprising means for cutting off a servo loop for a predetermined period of time when the absolute value of the output level exceeds a predetermined value, the device discharging the electric charge of the electricity storage element of the low-pass filter when the servo loop is cut off. A recorded information reading device characterized by having a discharge means.