JPS6319943Y2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an information reading device, and more particularly to an information reading device having a servo system for controlling the position of a pickup information detection point.

A so-called tracking servo device is used so that the information detection point of the pickup always accurately tracks the recording track on the recording surface. Furthermore, in order to correct and control the time axis of the reproduced information signal, it is necessary to control the movement of the information detection point in the tangential direction of the recording track, and a so-called tangential servo device is used.

The former tracking servo device will be explained using an optical information reading device as an example. FIG. 1 is a diagram schematically showing the block, in which an error signal corresponding to a positional deviation between a light spot as an information detection point and a recording track in a direction orthogonal to the track is generated from a well-known tracking error signal generator 1. be done. This error signal becomes an input to a drive amplifier 4 via an equalizer amplifier 2 and a loop switch 3. The output of the drive amplifier 4 becomes a drive signal for the drive coil 6 that controls the deflection angle of the information reading device 5 as an actuator. By controlling the deflection of the tracking mirror 5, the position of the information detection point can be moved in the direction perpendicular to the track, and accurate tracking operation can be performed. The system is stabilized by detecting the current flowing through the coil 6 with a resistor and feeding it back to the input of the drive amplifier 4 via the resistor 8 to form a negative feedback loop.

On the other hand, an LPF (low pass filter) 9 is provided which inputs the drive signal flowing through the drive coil 6.The level of this LPF output is judged by a window comparator 10, and when it exceeds a certain level range, a detection output is output from this comparator. is generated. In response to the timing of this detection output,
The MMV (monostable multivibrator) 11 is triggered and a single output with a constant width is generated. During the existence of the single output, the loop switch 3 is open and the tracking servo loop is disconnected.

In the configuration shown in FIG. 1, during normal playback, the loop switch 3 is on, and the tracking servo operates normally, so that the information detection point always accurately follows the recording track. Here, in order to search for recorded information, a so-called scan operation has been performed by fast forwarding the pickup in the radial direction of the recording disk (direction perpendicular to the track).
In this case, a fast forward operation is performed while the tracking servo loop is turned on, but since there is a limit to the deflection angle from the neutral point of the tracking mirror 5, which is an actuator for moving the information detection point, the limit angle It is necessary to return the tracking mirror 5 to the neutral point before reaching .

For this purpose, the DC component of the drive signal for coil 5 is
When the DC level detected by LPF9 exceeds the threshold range of window comparator 10,
Trigger MMV11, cut off the servo loop during the existence period of single pulse by this MMV, and mirror 5
returns to the neutral point. A sufficient time for the mirror to return to the neutral point is set by the time constant of the MMV 11, and when this period has elapsed, the servo loop is turned on again and scanning is performed while tracking.

In this method, the drive signal to the coil 11 is set to zero when returning the mirror to the neutral point, so the mirror current changes in steps when the loop is broken, and the response of the mirror depends on the actuator including the mirror. The return operation is determined by the characteristics. Since the characteristics of this actuator are expressed in a quadratic form, the movement of the mirror when the loop is broken results in damped oscillation as shown in FIG. 2A.
FIG. 2B is a chart showing the on/off timing of the loop switch 3. Because of this damped vibration,
The disadvantage is that it takes a considerable amount of time for the mirror to come to a complete stop. This phenomenon occurs not only in tracking servo systems but also in tangential servo systems.

In other words, if the DC component of the time axis error of the reproduced signal is superimposed during scan operation, the tangential servo loop is disconnected and the mirror is returned to the neutral point as soon as possible before the deflection angle of the tangential mirror reaches its limit value. The mirror needs to be restored. At this time as well, the mirror returns naturally by simply turning off the servo loop switch, which results in a long return time.

Furthermore, similar problems occur not only in optical information reproducing devices but also in other devices such as capacitance type devices.

SUMMARY OF THE INVENTION An object of the present invention is to provide an information reading device that can shorten the time required to return the deflection amount of an actuator that controls the movement of an information detection point to its initial value during a scanning operation or the like.

The information reading device according to the present invention disconnects the servo loop for the position movement servo of the information detection point when the amount of deviation from the predetermined position of the actuator for moving the pick-up information detection point exceeds a predetermined range. and means for generating a signal whose level gradually decreases from the signal level for driving the actuator immediately before the servo loop is broken, and this signal is used to drive the actuator during the loop break. It is characterized by

The present invention will be explained below using the drawings.

FIG. 3 is a block diagram of an embodiment of the present invention, showing a tracking servo system of an optical information reading device. Components equivalent to those in FIG. 1 are designated by the same reference numerals, and their description will be omitted. A series circuit including a power storage element 12 and a resistor 13 is provided between a signal line between the loop switch 3 and the drive amplifier 4 and a ground point. In addition, the electricity storage element 12
Resistors 14 and 15 are provided at the input of the drive amplifier 4 to form a discharge path.

In this configuration, when loop switch 3 is on, the series circuit of resistor 13 and power storage element 12 does not affect the servo loop. loop switch 3
When the loop switch is turned off, since the error signal immediately before the loop switch is turned off, that is, the signal for driving the mirror, is stored in the storage element 12, this stored charge is discharged with a predetermined time constant. Since the coil 6 is driven by this discharge current, a drive signal that gradually decreases in accordance with this discharge current flows to the actuator. In other words, if the DC component of the drive signal immediately before the loop breaks is V ₀ and the discharge time constant of the storage element is τ, then V ₀ ·ε−t/τ
This means that a signal has been applied, and the tracking mirror 5, which is an actuator, moves in accordance with the signal waveform.

Figure 4A is a waveform showing the movement of the tracking mirror, and there is no damped oscillation during the off period at the loop switch on-off timing in Figure B, and the time constant τ
Accordingly, the mirror performs a simple damping operation and quickly returns to the mirror neutral point.

FIG. 5 is a circuit block diagram of another embodiment of the present invention, and is shown in the case of a tangential servo system in an optical tracking servo.
A reproduced RF (high frequency) signal from the pickup 16 is amplified by an amplifier 17 and input to a demodulator 18 . A burst extractor 1 is used to extract a color burst signal from the color video signal that is the demodulated output.
9 is provided, and the time axis error signal generator 2
1, this burst signal is phase-compared with the reference signal from the reference signal generator 20, and then the comparison output is sampled and held to become time-base error information. This time axis error information is input to the drive amplifier 23 via the loop switch 22 and the resistor 31, and becomes a drive signal for the coil 25 that drives the tangential mirror 24. Resistors 26 and 27 constitute a feedback circuit to drive amplifier 23.

In this example as well, a series circuit of a power storage element 28 and a resistor 29 is provided between the output line of the loop switch 22 and the ground point, and the resistor 30 is connected to the resistor 2.
Together with 9, it forms a discharge path of the electricity storage element 28.
By doing so, the DC component of the error signal immediately before the loop switch 22 is turned off is stored in the storage element 28, and the electric charge in the storage element 28 is discharged with a predetermined time constant while the switch is turned off. Therefore, since a signal similar to this discharge waveform is applied to the coil 25, the tangential mirror 24 quickly returns to the neutral point without vibration.

The LPF 32, the window comparator 33, and the MMV 34 have the same functions as the LPF 9, the window comparator 10, and the MMV 11 shown in FIGS. 1 and 3, and therefore will not be particularly described.

In each of the above examples, a power storage element (capacitor) is used and its discharge time constant τ is used to drive the actuator while the servo loop is disconnected.When the servo loop is disconnected, this capacitor is discharged at a constant current and a signal with a constant slope is used to drive the actuator. It is good to drive.

As described above, according to the present invention, it is possible to significantly speed up the return of the actuator to the initial position for moving the information detection point with an extremely simple configuration. Therefore, it is possible to reduce image disturbance during the scanning operation and to increase the scanning speed. Also, at the resonant frequency, Q
Since the actuator returns to the initial position in a short time even if an actuator with a high resistance is used, there is no need to use a mechanical damper.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a conventional tracking servo system, FIG. 2 is a diagram showing the operation of the blocks in FIG. 1, FIG. 3 is a block diagram of an embodiment of the present invention, and FIG. FIG. 5 is a block diagram of another embodiment of the present invention. Explanation of symbols of main parts, 1... Tracking error signal generator, 3, 22... Loop switch,
5... Tracking mirror, 12, 28... Power storage element.

Claims (1)

[Claims for Utility Model Registration] (1) An information reading device having servo means for controlling the position of a pick-up information detection point, the amount of deviation of an actuator from a predetermined position to move the position of the information detection point. means for cutting off the servo loop of the servo means when the servo loop exceeds a predetermined range; and signal generating means for generating a signal whose level gradually decreases from the signal level for driving the actuator immediately before the servo loop was cut off. and an information reading device configured to drive the actuator while the servo loop is interrupted using a signal from the signal generating means. (2) The signal generation means has a storage element that stores a signal for driving the actuator immediately before the servo loop is disconnected, and the discharge signal of the storage element is used to drive the actuator. An information reading device according to claim 1. (3) The servo means is a tracking servo device that controls the movement of the spot light serving as the information detection point in a direction substantially perpendicular to the recording track, and the actuator includes a tracking mirror. Range 1 or 2
Information reading device described in section. (4) The servo means is a tangential servo device that controls the movement of the spot light serving as the information detection point in the tangential direction of the recording track, and the actuator includes a tangential mirror. The information reading device according to scope 1 or 2.