JPS6297140A - Driving method for optical pickup - Google Patents

Abstract

PURPOSE:To reduce the gain needed for a control loop by adding a feedforward circuit to the control loop. CONSTITUTION:The output delta of a position detecting means is used for feed forward and is multiplied by a transmission function K/KT and then applied to an adding point 104 of the 1st control loop 100. While a current (i) correspond ing to the drive current to be supplied to a tracking motor is transmitted to the right end of the point 104 and therefore multiplied by KT/KT to be fed forward to an adding point 204 of the 2nd loop. The output delta is multiplied by K/KT and fed forward to the point 204. The signal including the information the elastic reaction of a plate spring, etc. is applied to the tracking motor. While a seeking motor is controlled by the signal estimating the reaction of the driving force fp of an optical pickup as well as the reaction of the plate spring. Thus it is possible to reduce the gain needed to attain the same accu racy.

Description

[Detailed description of the invention] (Technical field) The present invention relates to an optical pickup driving method.

(Prior art) Optical pickups are disks in which information is written on tracks formed in spiral or concentric circles on an optical disk.
Alternatively, it is known as a device for reading out information written on a track.

In order to write or read information to or from an optical pickup, a seek operation to bring the optical pickup to a desired track position, a tracking operation to accurately maintain the positional relationship between the optical pickup and the track, and a read/write operation from the optical pickup are required. A focusing operation is required to focus the light onto the track.

The optical pickup is supported on a carriage, and seek operations are performed by moving the carriage.

A leaf spring is generally used to support an optical pickup on a carriage, but this leaf spring causes the following problems.

In other words, in the tracking operation, the tracking signal obtained from the optical pickup is fed back to the tracking motor, and the optical pickup is moved relative to the carriage.
Although this is done by relatively displacing the optical pickup, the required gain of the control loop for the tracking operation becomes high due to the elastic force of the leaf spring that supports the optical pickup.

In order to effectively solve such problems, the applicant must first
The following optical pickup driving system was proposed (Japanese Patent Application No. 153558/1982).

That is, this is a drive method that detects the amount of displacement of the optical pink-up relative to the carriage during tracking, feeds it back to the seek motor, and drives the carriage so that it follows the movement of the optical pickup.

(Objective) The present invention aims to provide a novel optical pickup driving method that can further improve the control loop gain reduction in the optical pickup driving method that causes the carriage to follow the movement of the optical pickup as described above. .

(composition) The invention will now be described.

An optical pickup driving device to which the present invention is applied includes an optical pickup, a carriage, a seek motor, a tracking motor, a position detection means, and a plurality of leaf springs.

The carriage is movable in a direction substantially perpendicular to the tracks on the optical disk, which is called the R direction, and is moved in the R direction by the seek motor.

The optical pickup is supported on the carriage by the plurality of leaf springs, and can be displaced in the R direction relative to the carriage by the bending of the leaf springs.

The tracking motor is mounted on the carriage and is used to displace the optical pickup in the R direction relative to the carriage. A tracking signal from the optical pickup is fed back to this tracking motor to form a control loop, and this control loop is referred to as a first control loop.

Next, the position detection means is provided on the carriage and detects the amount of displacement of the optical pickup in the R direction relative to the carriage.

The output of this position detection means is fed back to the seek motor during tracking, forming a control loop. This control loop will be referred to as a second control loop.

In the first control loop, the movement of the optical pickup relative to the carriage is controlled by the tracking signal, and in the second control loop, the movement of the optical pickup relative to the carriage is controlled by the output of the position detection means.
The movement of the carriage to follow the optical pickup is controlled.

Since the carriage moves to follow the optical pickup, the deflection of the leaf spring during the movement of the optical pickup for tracking is reduced, and the elastic force of the leaf spring is reduced, so the required gain in tracking control is reduced.

Now, in the present invention, in order to further suppress the decrease in the gain described above, the following steps are taken.

That is, (i) the output of the position detection means is fed forward to the first control loop; Ol) the signal corresponding to the drive current of the tracking motor is fed forward to the second control loop; (ii) Either the output of the position detection means is fed forward to the second control loop, or both of these feedforwards are performed.

This will be explained below using a specific example.

FIG. 2 shows an example of an optical pickup drive device to which the present invention is applied.

The optical pickup 10 having a focusing function has an objective lens 12 and four leaf springs 14A.

Carriage 16 by 14B, 14C, 14D
The IC is supported and can be displaced in the ICR direction relative to the carriage 16 due to the deflection of a leaf spring 14A or the like.

A tracking motor 22 is mounted on the carriage 16 to displace the optical pickup 10 in the R direction within the range of deflection of the leaf spring 14A and the like.

The tracking motor 22 is a linear motor, the magnet and yoke are fixed to the carriage 16, and the coil is fixed to the optical pickup 10.

Further, a light shielding plate 24 fixed to the optical pickup 10,
A sensor 26 fixed to the carriage 16 constitutes position detection means. This position detection means will be described in detail later.

The carriage 16 includes two rods 18A parallel to the R direction,
18B via linear bearings 2OA and 20B, and is movable in the A and R directions.

A coil 28 is also fixed to the carriage 16, and the coil 28 is passed through the yoke 30 in the R direction.

A yoke 32 is arranged parallel to the yoke 30, and a plate-shaped magnet 34 is fixed to the surface of the yoke 32 on the yoke 30 side.

The yokes 30, 32, the magnet 34, and the coil 28 constitute a seek motor. That is, the magnet 34 is magnetized in the thickness direction, and a uniform magnetic field is formed between the yoke 30 and the magnet 34. Coil 28 crosses this magnetic field, so passing current through coil 28 causes R
An electromagnetic force in the direction is generated, and the carriage is moved in the R direction.

Now, a linear scale 36 is arranged parallel to the R direction, and a linear sensor for reading the linear scale 16 is mounted on the carriage 16. j-38 is fixedly installed.

Next, the position detection means will be explained with reference to FIGS. 3 and 4.

As mentioned above, the position detection means is composed of the light shielding plate 24 fixed to the optical pickup 10 and the sensor 26, and the sensor 26 is, as shown in FIG.
Light emitting element 26A, light receiving element 26B, and slit plate 2
It has 6C.

When the optical pickup 10 is at the reference position with respect to the carriage 16, in other words, when the optical pickup 10 is not displaced in the R direction relative to the carriage 16, the tip of the light shielding plate 24 is It is located at the center of the slit of the slit plate 16C.

In FIG. 4, reference numeral 26C1 indicates a slit in the slit plate 26C. Assuming that the horizontal direction is the position of the tip of the light shielding plate 24, this position change causes the light receiving element 26B to
The output changes as shown in song @F in FIG. Therefore, the output of the position detection means, that is, the output of the light receiving element 26B is F.
If o, then the optical pickup 10 is at the reference position with respect to the carriage 16, and the relative displacement amount in the R direction with respect to the carriage 16 is zero.

Now, in the apparatus shown in FIG. 2, considering the X axis in the R direction, the X coordinate of the carriage 16 and the X coordinate of the XCS optical pickup 10 are assumed to be Xp. Furthermore, in a state where the leaf spring 14A etc. are not bent, in other words, when no elastic force is generated by the leaf spring, Xp=xc.

Then, if the composite spring constant of the leaf spring 14A etc. is K, then
The elastic force due to the leaf spring 14A and the like is given by δ to −, where δ=Xp −Xc.

Next, let the mass of the carriage 16 be Mc, the mass of the optical pickup 10 be Mp, the force acting on the optical pickup 10 from the tracking motor 22 be fp, and the force acting on the carriage 16 from the seek motor be fc.

Then, the motion equation for the optical pickup 10 is as follows.

becomes. Further, the equation of motion for the carriage 16 is -. The first and second terms on the right side of equation (2) are the optical pickup 1
It is the reaction force due to 0.

In equation (1), in order to set K so that the force (- δ) can be ignored, (Kδ) can be added to the right side of equation α).

Since δ is the difference between Xp and Xc, that is, the output of the position detection means, δ can be realized by multiplying this output by .

Next, in equation (2), in order to set K so that CKf−fp) can be ignored, it is sufficient to add (− to δ+fp) to the right side of equation (2). (− to δ) of (− to δ+fp)
can be realized by multiplying the output of the position detecting means by (-K). fp is the force generated by the tracking motor 22, but if the drive amplifier for this motor is a current source type, the force (jp) is proportional to the current value of this amplifier output, so this current value fp can be realized by multiplying the output by a constant.

In this way, δ and fp can be realized by the circuit, so by appropriately feeding forward these quantities, we can create a control system that can ignore (δ) and (Kδ-jp). Can be configured. In this control system, the right side of equation (1) is only fp, and the right side of equation (2) is only fc,
Control can be performed while ignoring the reaction force caused by the leaf spring and tracking motor, and the loop gain required to achieve the same accuracy can be kept small.

FIG. 1 is a block diagram showing control of the optical pickup driving method of the present invention. 100 is a first control loop;
Reference numeral 200 indicates a second control loop.

The transfer function KT is the thrust constant of the tracking motor, and the transfer function KS is the thrust constant of the seek motor.

The tracking signal α obtained from the optical pickup is the first
The phase of the signal is compensated by the phase compensation circuit 102 of the control loop, and the signal is applied to the tracking motor 22 (FIG. 2).

The line with transfer constant K in the control loop system is the transfer function of the control loop system according to the equation α). The operation of the tracking motor 22 causes the optical pickup 10 to be displaced. Since the difference between the coordinate Xp and the trajectory γ on the disk plate becomes the tracking signal α, control is performed so that this α becomes O. - On the other hand, the output δ of the position detection means is phase compensated by the phase compensation circuit 202 of the second control loop 200 and applied to the seek motor.

Transfer function and feed path SM of Xp
A line having a transfer function K in a linear system on c+ is a transfer function according to equation (2). The difference between the output Xc and XpO is the output δ of the position detection means.

Now, in FIG. 1, for the sake of clarity, the route shown with a thick line indicates the feedforward of the present invention.

The output δ of the position sensing means is applied to a summing point 104 of a feedforward control loop 100. On the other hand, what is transmitted to the right side of the summing point 104 is feed forward to the summing point 204 of the 1 control loop corresponding to the drive current to the tracking motor. Further, the output of δ is multiplied by -s and fed forward to the summing point 204.

Since the signal is fed forward to the point 104, a signal containing information about the elastic reaction force of the leaf spring 14A etc. is applied to the tracking motor. The pickup 10 is driven. As a result, the influence of the elastic reaction force can be ignored, and as a result, the required loop gain of the first loop 100 can be kept small.

Similarly, a signal corresponding to the drive current of the tracking motor is fed forward to the second control loop 200, and a signal based on the reaction force of the leaf spring is also fed forward to the second control loop 200. Since the control is performed using a signal that takes into account the reaction of the pickup driving force fp and the reaction force of the leaf spring, the decrease in gain due to these reactions and reaction force y can be kept small.

In this example, three feedforwards were performed, but even performing only one feedforward has the effect of suppressing the decrease in gain. In other words, if feedforward is performed only to the first control loop 100, the reduction in gain caused by the elastic reaction force of the leaf spring can be suppressed in the first control loop, and the gain in the second control loop 20 can be suppressed.
By performing feedforward only to 0, the decrease in gain in the second control loop can be kept small.

FIG. 5 shows a push circuit diagram corresponding to the control block diagram of FIG. 1.

The output of the optical pickup 10 is amplified by an amplifier (not shown) and applied to an analog arithmetic circuit 50Vc for arithmetic processing to produce a data signal and a focusing signal SF.

A tracking signal α is generated from an analog calculation circuit 50. The focusing signal SF is the optical pickup 1
The linear motor feeds the focusing linear motor built into the lens 0, and the linear motor feeds the objective lens 12 (second
) in the optical axis direction.

On the other hand, the tracking signal α is input to the phase compensation circuit 102 and subjected to phase compensation. Light shielding plate 24 and sensor 26 (second
After being amplified by an amplifier (not shown), the output of the position detection means 54 configured as shown in FIG. be done.

The output thereof is added to the output of the phase compensation circuit 102 and applied to the current source type servo amplifier 56 of the tracking motor. Reference numeral 58 is a coil of a tracking motor. Due to the resistor 64, a voltage signal proportionally corresponding to the drive current of the tracking motor is generated at point P, and is applied to the gain amplifier 60.

The output of the phase compensation circuit 202 is applied to the gain amplifier 52-2 servo amplifier ωA, and the output is energized to the coil 62 of the seek motor. Reference numeral 66 is a resistor.

The gain amplifier 52-1 is for feed forward to the first control loop, and the gain amplifier 6o and 52-
2 is for feedforward to the second control loop. In either feedforward, the gain amplifier (5
2-1, 52-2, 60) output and phase compensation circuit (
162, 202) are added, and a specific circuit example of this part is shown in FIG. Code 70.80
are operational amplifiers, symbols R1, R2, R3, R4, 72,
74, 76, and 78 indicate resistance. However, resistance 74.7
Let R be the resistance value of 8.

Input voltage, vlt v, l v4s output voltage, v3
shall be. vl is the output of the gain amplifier (52-1, 60), and 2 is the output of the phase compensation circuit (102, 202). Output v3 is applied to servo amplifier 61.

(Effects) As described above, according to the present invention, a novel optical pickup driving method in an optical pickup driving device can be provided.

With this method, the required gain of the control loop can be effectively kept small.

[Brief explanation of drawings]

FIG. 1 is a control block diagram showing one embodiment of the present invention, FIG. 2 is a perspective view showing an example of a vertical optical pickup driving device to which the present invention is applied, and FIGS. 3 and 4 show the position 5 is a block circuit diagram corresponding to the embodiment shown in FIG. 1, and FIG. 6 is a circuit diagram showing a specific configuration of the characteristic parts of the circuit shown in FIG. 5. be. 10... Optical pickup, 14A, 14B,
14C, 14D... Leaf spring, 16... Carriage, 2
2... Tracking motor, 24... Light shielding plate,
26... Sensor, 100... First control loop,
200...Second control loop. Steam Gin

Claims (1)

[Scope of Claims] A carriage movable in the R direction substantially orthogonal to the tracks on the optical disk, a seek motor for moving the carriage in the R direction, an optical pickup, and the optical pickup mounted on the carriage. a plurality of leaf springs supported on the carriage so as to be movable in the R direction relative to the carriage; and a tracking member provided on the carriage for displacing the optical pickup in the R direction relative to the carriage; It has a motor and a position detecting means for detecting the amount of displacement in the R direction relative to the carriage of the optical pickup, and the output of the position detecting means is fed back to the seek motor during tracking. In the optical pickup driving device, the movement of the carriage follows the movement of the optical pickup; (b) Feedback a signal corresponding to the drive current of the tracking motor to the second control loop that feeds back the output of the position detection means to the seek motor; c) Feedback the output of the position detection means to the second control loop, or (d) or perform each of the feedforwards in (a), (b), and (c) above together. An optical pickup driving method characterized by: