JPH0322674B2 - - Google Patents

Description

[Detailed description of the invention]

FIELD OF INDUSTRIAL APPLICATION The present invention relates to an information reproducing device for reading information from a record carrier having information tracks. Configuration of conventional examples and their problems Information reproducing apparatuses that read information from an information track by rotating a record carrier having an information track or an information reading head include magnetic disks, magnetic drums, floppy disks, and rotating head types. Video tape recorders, and optical types such as video disk players and compact disk players are known. These information reproducing devices require accurate tracking control as the recording density increases. However, if a disturbance is introduced into the tracking control system, such as when there is a defect on the record carrier, the tracking control is disturbed and the track tends to jump to a nearby track. This tendency is particularly pronounced in optical compact disc players, etc., where the track linear velocity is slow, because the passage time through the defective portion is long. In order to improve such a part, a method has conventionally been used in which integral compensation is applied to the tracking control to substantially reduce the high-frequency gain. FIG. 1 is a block diagram showing an example of a tracking control system of a conventional information reproducing apparatus using the above method, in which 1 is an information track, 2 is an information reading head, 3 is a tracking processing means, 4 is a loop switch, and 2 is a tracking control system. is a differential compensation circuit, 6 is an integral compensation circuit, and 7 is an actuator. The operation of the conventional tracking control system configured as described above will be explained below. The information reading head 2 detects a relative positional error with the information track 1 and outputs a tracking error signal. At this time, the relative position error may be detected by optical, magnetic, or other methods. The tracking processing means 3 outputs a driving voltage for moving the information reading head so as to minimize the tracking error signal. A loop switch 4 is used to turn tracking control on and off.
The differential compensation circuit 5 creates a sufficient phase margin so that the tracking control system does not oscillate, and the integral compensation circuit 6 functions to obtain sufficient low-frequency gain without increasing the high-frequency gain and to reduce steady-state errors. The actuator 7 moves the reading head using the drive voltage that is the output of the tracking processing means 3.
Keep the relative position with the information track constant. However, in the conventional example described above, due to the transient characteristics of the integral compensation circuit, excessive voltage may be applied to the actuator when the power is turned on or when the loop switch 4 is closed, and the tracking control system may not be able to pull in the tracking control system stably. The problem was that it was not possible to apply a sufficient amount of integral compensation. Purpose of the Invention The purpose of the present invention is to eliminate the above-mentioned conventional drawbacks, to enable stable tracking control even when a large disturbance is mixed into the tracking error signal due to scratches on the record carrier, and to enable stable tracking control when the power is turned on. It is an object of the present invention to provide an information reproducing device that has excellent transient characteristics of a control system, such as immediately after turning on a loop switch. Structure of the Invention The information reproducing apparatus of the present invention includes an information reading head that reads information from a record carrier having an information track, detects a relative position error with the information track, and outputs a tracking error signal; An actuator that moves the
Tracking control means is provided for applying a drive voltage to an actuator to move the information reading head so as to minimize the relative position error from the tracking error signal, and the tracking control means includes rotation of the record carrier or the information reading head. It has a resonant circuit composed of a switched capacitor filter having a resonant frequency almost equal to the frequency, and the clock of the switched capacitor filter is synchronized with the frequency generator output of the motor that rotates the record carrier or the information reading head. This enables stable tracking control even when a large disturbance is mixed into the tracking error signal due to scratches on the record carrier, and it also enables stable tracking control when the power is turned on or the loop switch is turned on. This is to prevent problems with transient characteristics of the control system immediately after the control system is turned on. DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 2 shows a block diagram of a tracking control system in an embodiment of the present invention. 1 is an information track, 2 is an information reading head, 3 is a tracking processing means, 4 is a loop switch, 5 is a differential compensation circuit, 7 is an actuator, 8 is a resonant circuit constituted by a switched capacitor filter, 12 is a motor, and 13 is a frequency generator. The operation of the tracking control system of the information reproducing apparatus of this embodiment configured as described above will be described below. The information reading head 2 reads information from the information track 1 and outputs a tracking error signal indicating how much the information reading head 2 is relatively deviated from the positional relationship with the track 1 where information is most easily read. At this time, magnetic methods, optical methods, methods using capacitance, etc. are generally known for detecting information or tracking error signals, and any of these methods may be used. The tracking error signal is input to the tracking control means 3, and generates a voltage for driving the actuator 7. The actuator 7 moves the information reading head 2 using the driving voltage of the tracking control means 7, and pulls the information reading head 2 back from the track 1 to a position where it is easiest to read information. The tracking error signal is input to the differential compensation circuit 5 through the loop switch 4. The output of the differential compensation circuit 5 is input to a resonant circuit 8 constituted by a switched capacitor filter. This switched capacitor filter uses a signal synchronized with the output of the frequency generator 13 of the motor 12 that rotates the disk as a clock, and increases only the gain near the motor rotation frequency of the tracking control system. Figure 3 shows typical transfer characteristics of each part of the tracking control system. FIG. 3a shows the transfer characteristic of the actuator 7, FIG. 3b shows the transfer characteristic of the differential compensation circuit 5,
FIG. 3c shows the transfer characteristic of the resonant circuit 8 constituted by a switched capacitor filter, and FIG. 3d shows the open-loop transfer characteristic of the tracking control system. In general, the tracking error signal contains many eccentric components caused by rotation of the record carrier or read head. Especially as recording density increases,
As the information track interval becomes narrower, the proportion of eccentric components included in the tracking error signal increases. For example, in the case of a compact disc player, the total eccentricity of the disc, motor, and turntable is 100 μm, while the information track interval is 1.6 μm. Therefore, in order to reduce the tracking error and cause the information reading head to follow the information track, it is necessary to increase the gain in the vicinity of the motor rotation frequency of the tracking control system. Conventionally, an integral compensation circuit has been used to increase the gain of the entire low frequency region, including eccentric components. However, the integral compensation circuit has had problems such as excessive voltage being applied to the actuator due to the transient characteristics of the integral compensation circuit when the power is turned on or off or when the loop switch is turned on or off. The resonance circuit 8, which is composed of a switched capacitor filter, creates a sharp resonance near the motor rotation frequency and increases the gain of the entire tracking control system at the eccentric frequency.Since the gain is increased only at a specific frequency, transient It has excellent characteristics. FIG. 4 is a circuit diagram of a specific embodiment of the resonant circuit 8, and 9 is a high-pass filter 10 consisting of a switched capacitor filter.
is an operational amplifier. The transfer function H(S) of the high-pass filter has its cutoff angular frequency ω ₀ , Q
When is Q ₀ , it is expressed as H(S)=S ² /S ² +ω ₀ /Q ₀ S+ω ₀ ² ...(1), so the overall transfer function G(S) is

[Formula] Q ₁ = ω ₀ /Ω ₀ Q ₀ , then G(S) = −R _f /R _i・R _s /R _s +R _f・S ² +ω ₀ /Ω ₀ S+ω ₀ ² /S ² +Ω It is expressed as ₀ /Q ₁ S + Ω ₀ ² ...(2). Here, by approximately matching Q ₀ and ω ₀ to the Q and resonance angular frequency of the actuator 7 and Ω ₀ to approximately the motor rotational angular frequency, the characteristics shown in FIG. 3c are obtained. By suppressing the resonance of the actuator 7, the transient characteristics are improved, and even when the tracking control system is opened, it causes free vibration at the motor rotational angular frequency, which has the advantage of making it difficult for the actuator to separate from the track. If it is relatively small, a filter having a resonance point only at the eccentric frequency may be used. For convenience of explanation, this embodiment assumes a device that reads information written on a rotating disk, but the present invention is not limited to this, and for example, a device such as a video tape recorder in which a reading head is read out while rotating on a track is assumed. It is clear that the same approach can be taken in the case of tracking. Since the resonant frequency of the switched capacitor filter changes in exact proportion to the clock, it accurately follows fluctuations in the motor's rotational speed. Therefore, the resonant frequency can always be precisely matched with the motor rotation frequency. In this embodiment, a high Q can be achieved at the motor rotation frequency.
This method has the advantage that the same effect can be obtained even when the rotational speed of the motor changes, such as in the case of a recording method in which the linear velocity is constant. Effects of the Invention As is clear from the above description, the present invention provides an information reading head that reads information from an information track on a record carrier and outputs a tracking error signal, an actuator that moves the information reading head, and an actuator that reads information from an information track on a record carrier and outputs a tracking error signal. Tracking control means for applying a driving voltage to the actuator to move the information reading head so as to minimize the relative positional error between the information track and the information reading head, and the tracking control means is provided with a tracking control means for applying a driving voltage to the actuator to move the information reading head so as to minimize a relative positional error between the information track and the information reading head. It has a resonant circuit constituted by a switched capacitor filter having a resonant frequency approximately equal to the rotational frequency of the read head, and the clock of the switched capacitor filter is set at the frequency of the motor that rotates the record carrier or the information read head. Since it is configured to synchronize with the generator output, turning on the power,
It is possible to stably suppress the eccentric component of the tracking error signal based on the rotation of the information reading head or record carrier without impairing the transient characteristics when the loop switch is turned off or on or off, thereby eliminating scratches on the record carrier. It does not disturb the tracking control system, and even when the motor rotation speed changes, such as when the motor starts up or in the case of a constant linear velocity recording method, it follows changes in the motor rotation speed and remains stable. It can be made with a servo system. In addition, since it is configured with a switched capacitor filter, it is possible to configure a high Q filter precisely at the motor rotation frequency, and the above effect can be obtained even when the rotation speed of the information reading head or recording carrier fluctuates. It will be done.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing an example of a tracking control system of a conventional information reproducing device, Fig. 2 is a block diagram showing an embodiment of the present invention, and Fig. 3 is a typical transfer characteristic of each part of Fig. 2. FIG. 4 is a specific circuit diagram of the main parts of FIG. 2. DESCRIPTION OF SYMBOLS 1... Information track, 2... Information reading head, 3... Tracking processing means, 4... Loop switch, 7... Actuator, 8... Resonance circuit, 9... High pass filter, 10... Operational amplifier , 12... motor, 13... frequency generator.

Claims (1)

[Claims] 1: an information reading head that reads information from a record carrier having an information track, detects a relative position error of the information track, and outputs a tracking error signal; an actuator that moves the information read head; tracking control means for applying a drive voltage to the actuator to move the information read head in such a manner as to minimize relative position errors; It has a resonant circuit constituted by a switched capacitor filter having a resonant frequency, and the clock of the switched capacitor filter is synchronized with the frequency generator output of the motor that rotates the record carrier or information read head. An information reproducing device characterized by: