JPH01182978A - Servo circuit for disk player - Google Patents

Abstract

PURPOSE:To prevent the generation of the reading errors of a jumping-up and the like even when a vibration is given to a pickup from a driving mechanism by increasing a track following capacity of the pickup with increasing the gain of a servo circuit at the time of a pickup moving. CONSTITUTION:When a motor driving circuit inputting voltage necessary to move the pickup exceeds a reference voltage, the output of a comparison circuit 7 inverts from an H level to an L level and turns off the switching transistors Q1 and Q2 of a focus and tracking gain changing circuits 8 and 9. Consequently, gain values R3 and R6 decided by resistors R1-R6 are increased by cutting off and the response of an objective lens to a focus error signal and a tracking error signal turns to be good. Thus, a reading point is kept on the track and the track can be followed well, even when the vibration generated at the time of an optical pickup 1 moving is given to the objective lens.

Description

Detailed Description of the Invention (a) Industrial Application Field The present invention relates to a tracking servo circuit used in a compact disc player (hereinafter abbreviated as CD player), etc.
Alternatively, the present invention relates to an improvement in a servo circuit arranged for track scanning, such as a focusing servo circuit.

(b) Conventional technology As is well known, a CD player uses a tracking servo to accurately trace pit rows (tracks) carved in a spiral pattern from the inner circumference to the outer circumference of the disk, and at the same time to prevent surface runout of the disk. reads and reproduces recorded digital signals using a laser beam while always keeping the camera in focus using a focusing servo. Additionally, a pickup feed mechanism is provided to trace the disk from the innermost track to the outermost track. This is done by detecting the DC component of the tracking error signal, increasing the voltage, and applying it to the pickup feeding motor to move the pickup in the radial direction.

By the way, when the pickup is moved, vibrations are generated by the motor, speed reduction mechanism, etc., which are transmitted to the objective lens of the pickup and cause disturbances to the servo circuit, resulting in various reading errors such as needle skipping. It is possible to reduce the transmission of vibration generated by the motor by setting a large reduction ratio of the reduction mechanism, but if the reduction ratio is set to a large value in this way, the pickup cannot be moved between the innermost and outermost peripheries. A problem arises in that it takes a lot of time to do so, which increases the access time. Therefore, it is not possible to set a reduction ratio that sufficiently suppresses vibrations transmitted to the pickup.

In addition, by increasing the gain of the servo circuit, the track following ability of the pickup can be increased, thereby minimizing the influence of the above-mentioned disturbance, but increasing the servo gain in this way can cause scratches, dirt, etc. on the disk. The servo circuit follows this, which may cause malfunctions such as track jumps. For this reason, the gain of the servo circuit cannot always be set high.

Q. Problems to be Solved by the Invention The present invention aims to prevent reading errors such as needle skipping from occurring due to vibrations generated in the pickup sliding mechanism during pickup movement.

B) Means for Solving the Problems In view of the above problems, the present invention provides a servo circuit for a disk player that reads and reproduces information by scanning information tracks recorded in a spiral pattern or concentric circles on a disk.
a tracking error signal creation circuit that creates a tracking error signal; a pickup drive circuit that moves a pickup in the radial direction of the disk based on a DC component of the tracking error signal created by the tracking error signal creation circuit; a comparator circuit that outputs a control signal when a predetermined level voltage is exceeded; and a gain of a servo circuit arranged to accurately scan the information track in response to the control signal output from the comparator circuit. The structure is equipped with a gain changing circuit to increase the gain.

2) Function: When the pickup is moved, the gain of the servo circuit is increased and the track following ability of the pickup is increased, so even if vibrations are applied to the pickup from the drive mechanism, reading errors such as needle skipping do not occur.

(f) Example In Fig. 1, the signal obtained by the optical pickup (1) is amplified and voltage converted by the preamplifier (2), and then contains data such as a tracking error signal, a focus error signal, and a music signal. It can be divided into high frequency signals. The preamplifier (2) also includes a laser diode drive circuit and a laser light output control circuit. Preamplifier (2)
The tracking error signal and focus error signal obtained in the above are applied to the respective gain change circuits (81f91 after being adjusted to appropriate voltages) and then applied to the tracking coil and focus coil drive circuit 00) α1), and then the optical pickup (1) The objective lens is electromagnetically driven in the tracking direction and the focusing direction. As reading progresses, the objective lens is gradually moved in the disk outer circumferential direction 1, and in response, the DC component of the tracking error signal gradually increases.

Further, the tracking error signal is converted into direct current by a low-pass filter (4) and applied to a motor drive circuit (5). As mentioned above, the DC component of the tracking error signal is
Gradually thickens (becomes light pickup (1) to motor (6)
When the torque required to move the optical pickup (1) reaches a level that generates enough torque to move the optical pickup (1), the optical pickup (1)
Track driven, objective lens is optical pickup (1)
Returns to neutral position. (7) is a comparison circuit that compares the voltage applied to the motor drive circuit with a reference voltage set slightly smaller than the motor drive circuit input voltage necessary for the pickup to move. The decoy is the spindle motor α that drives the turntable on which the disc is installed.
This is a spindle motor drive circuit that controls J.

When the motor drive circuit input voltage (DC component) exceeds the reference voltage, the output of the comparator circuit (7) is inverted from the H level to the L level, causing the switching of the focus and tracking gain changing circuits (8) and (9). Transistor (Ql)
(Q2) is turned off. For this reason, resistors R1, R2,
The gain values determined by R3, R4, R5, and R6 are increased by cutting off R3 and R6, thereby improving the response of the objective lens to the focus error signal and tracking error signal. Therefore, even if vibrations generated when the optical pickup (1) moves are applied to the objective lens, the reading point will not deviate from the track, and the track can be followed well.

It goes without saying that the present invention is not limited to the above embodiments and can be modified in various ways.

(g) Effects of the Invention As described above, according to the present invention, even if vibrations generated during pickup drive are applied to the pickup, a good reproduction operation can always be achieved without causing reading errors such as needle skipping.

[Brief explanation of the drawing]

FIG. 1 is a circuit configuration diagram showing an embodiment of the present invention. (1)...Optical pickup, (4)...Low pass filter, (5)...Motor drive circuit, (7)...
Comparison circuit, (8)...Focus gain change circuit, (
9)...Tracking gain change circuit, α0)...
Focus coil scolding circuit, (11)...tracking coil drive circuit.

Claims (1)

[Claims] (1) A servo circuit for a disc player that reads and reproduces information by scanning information tracks recorded in a spiral or concentric pattern on a disc, and includes a tracking error signal creation circuit that creates a tracking error signal; a pickup drive circuit that moves the pickup in the radial direction of the disk based on the DC component of the tracking error signal created by the tracking error signal creation circuit; and a pickup drive circuit that outputs a control signal when the DC component exceeds a predetermined level voltage. A servo circuit for a disc player, comprising: a comparison circuit; and a gain change circuit that increases the gain of the servo circuit in response to the control signal output from the comparison circuit.