JPH02302936A - Optical pick-up driving device - Google Patents

Abstract

PURPOSE:To compensate a frequency band with a turbulent displacement characteristic, to obtain a flat frequency characteristic and to execute a stable servo by making the ratio of the driving currents of a second actuator and a first actuator into the ratio of the acceleration current sensitivity of the first actuator to the acceleration current sensitivity of the second actuator. CONSTITUTION:For a lens holder 2, two pairs of elastic supporting members 30 are fitted to be mobile in an optical axis direction, the edges are fixed to an elastic supporting member holding part 4 to be raised on an actuator base 5. The ratio of a control current given to a second actuator 25 to the control current given to a first actuator 26 is adjusted to the ratio of the acceleration current sensitivity of the first actuator 26 to the acceleration current sensitivity of the second actuator 25 including the mass of the second actuator 25. Thus, the turbulence of the displacement characteristic in the tracking direction of the second actuator generated by executing the tracking by means of the first actuator can be solved, and a stable servo characteristic to truly trace even a high frequency can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a drive device for an optical pickup for reproducing or recording an optical disc such as a compact disc, write-once type, or rewritable type.

[Conventional technology]

FIG. 4 shows an example of the configuration of an optical pickup.

This example is suitable for using the optical disk system as a terminal storage device for a computer, and the optical pickup is divided into two parts in order to shorten access time. One fixed part 23 includes most of the optical system, such as a laser, a detector, a collimating lens, and a prism, and the other movable part 24 includes a first actuator 25 for track access and trunking, and for focusing. It is configured by a second actuator 26 for.

The first actuator is movable in the tracking direction along the slide shaft 27 by a magnetic circuit and coil (not shown), and the second actuator is movable in the tracking direction by a magnetic circuit and coil (not shown) provided on the first actuator. , a lens holder 2 to which an objective lens 1 is attached.
is connected to the spring holding part 4 provided on the actuator base 5 by an elastic support member 30 so that it is movable only in the focus direction.

The light beam emitted as parallel light from the fixed part is bent by 90 degrees by the reflecting mirror 28, passes through the objective lens l, and is focused on the disk 21 rotating around the rotation axis 22. The light beam reflected by the disk 21 passes through the same path and is separated into a signal and signals for focus and tracking control at the fixed part 23.

A focus control signal is applied to a drive section (not shown) of the second actuator so that the beam narrowed by the objective lens is always focused on the disk surface. A signal for tracking control is applied to the drive (not shown) of the first actuator so that the beam spot is always on the signal trunk. Further, the movable range of the first actuator is approximately the radius of the optical disc, and track access is also performed using this.

As described above, in this conventional example, since the objective lens 1 and the reflecting mirror 28 move simultaneously during tracking, there is an advantage that the optical axis does not shift as compared to a method in which only the objective lens is driven.

[Problem to be solved by the invention]

However, since the force applied to the first actuator is transmitted to the objective lens via the elastic support member,
At high frequencies, the objective lens becomes unresponsive to driving. In order to avoid this, it was necessary to make the second actuator lighter and to reduce the compliance of the elastic support member in the tracking direction.

However, with the above solution, the resonance generated between the drive coil of the first actuator and the actuator base was transmitted to the objective lens, and the frequency characteristics of the objective lens in the tracking direction could not be flattened, as shown in Figure 5. .

[Means to solve the problem]

Therefore, the optical pink amplifier driving device according to the present invention includes a first actuator that performs track access and tracking, the first actuator is connected to the elastic support member, and the objective lens is focused with respect to the first actuator. and an optical pickup having a second actuator that can be driven in the tracking direction, the first actuator and the second actuator are each provided with a constant current source for driving, and the driving current of the second actuator and the first actuator is The present invention is characterized in that the ratio is the acceleration current sensitivity of the first actuator including the mass of the second actuator to the acceleration current sensitivity of the second actuator.

[Effect]

Therefore, the disturbance in the displacement characteristics of the second actuator in the tracking direction caused by tracking with the first actuator is absorbed by the elastic support member,
The tracking drive means of the second actuator compensates for the frequency band in which the displacement characteristics are disturbed, thereby obtaining flat frequency characteristics and performing stable servo.

〔Example〕

FIG. 1(a), fb) shows an embodiment of the present invention.

In the figure, an objective lens l is attached to a lens holder 2. A pair of hollow, rectangularly wound focus coils 8 are attached to the lens boulder 2 with the objective lens 1 in between, in order to drive the objective lens 1 in the optical axis direction. Two square tracking coils 9 are attached to the winding surface of the focus coil 8. The central axis of the tracking coil 9 is
The focusing coil 8 is attached so as to be perpendicular to a plane including the central axis thereof.

The lens holder 2 equipped with the objective lens 1, the focus coil 8, and the tracking coil 9 has two sets of parallel elastic support members 30 that are movable in the optical axis direction.
Activate that edge and stand from Eta Base 5.''
It is fixed to the elastic support part +4 holding part 4. Furthermore, pairs of magnetic yokes 6a, 6b, 6c, and 6d are raised from the actuator base 5. The magnetic q-reflectors 5a and 6b are located in the hollow portion of the focus coil 8 and are configured not to come into contact with the movement of the lens holder 2 in the optical axis direction. There are magnetic yokes 5c and 5d, to which magnets 7a and 7b are attached, facing the magnetic yokes 6a and 6b, and generate parallel magnetic flux.

A focus coil 8 and a tracking coil 9 are arranged so as to interlink with this magnetic flux, and driving forces in the focus direction and the tracking direction can be obtained by supplying a control current.

The elastic support member 30 uses a plate spring in this example,
A part thereof has a semicircular curved part 33. The first actuator section 25 is configured to move the second actuator section 26 in the tracking direction to perform tracking and track access, and any method can be used.

In the above configuration, the drive section of the first actuator (
The displacement characteristics of the objective lens 1 in the tracking direction due to the tracking control current applied to the
become that way. This is because the semicircular curved portion 33 of the elastic support member 30 increases the compliance in the tracking direction, making it difficult for high frequency vibrations to be transmitted to the objective lens 1. Therefore, disturbances in the displacement characteristics due to resonance occurring between the drive coil of the first actuator and the actuator base are also less likely to be transmitted to the objective lens 1.

Furthermore, by supplying a control current to the tracking coil 9 provided in the second actuator, the displacement characteristics shown in FIG. 243 can be obtained. and adjusting the ratio of the control current applied to the second actuator and the control current applied to the first actuator to the ratio of the acceleration current sensitivity of the first actuator to the acceleration current sensitivity of the second actuator, including the mass of the second actuator. Accordingly, the displacement characteristic 41 shown in FIG. 2 can be obtained. Therefore, it is possible to solve the problem of the disturbance of the displacement characteristic caused by the abnormal resonance 44 shown in FIG.

The above-mentioned configuration will now be explained with reference to the equivalent circuit Q shown in FIGS. It becomes like the formula below.

Here, m, ... mass of the first actuator moving part m2
...Second actuator movable part mass C...Tracking direction compliance r of the elastic support member...Mechanical resistance F1 of the elastic support member...Driving force F2 of the first actuator...Second
Actuator driving force (trunking direction) In equation (1), the displacement frequency characteristic of the objective lens is simply -12
It can be seen that the characteristic is dB10ct, and no disturbance occurs in the amplitude 1 phase.

By the way, F + = A II + −−−−−−−−−−
−−−−−−−−−−−−−(41F t =A z
I z −−−−−−−−−−−−−−−−
−−−−−−−−−−−−−−(5) Here, A1...the force coefficient of the first actuator■,...the first
Drive current A2 of the actuator... Force coefficient of the second actuator ■2... Drive current of the second actuator, so the conditions of equation (2) are as follows.

A.

The force coefficient/mass on the right side of equation (6) indicates the acceleration sensitivity of the actuator to the current.

That is, the ratio of the drive currents of the second actuator and the first actuator is expressed as the acceleration current sensitivity of the first actuator including the mass of the second actuator AI/(m, 10 m,) to the acceleration current sensitivity of the second actuator Ax/mz If so, equation (2) is satisfied, and therefore the frequency characteristic becomes flat as shown in equation (3).

What determines this acceleration current sensitivity is the force coefficient and mass, as described above. Of these, the mass can be precisely designed in advance, but the force coefficient is determined by the magnetic flux density of the actuator's drive section and the effective length of the coil, and since the magnetic flux density fluctuates due to variations in the magnetic circuit components, it cannot be a constant value. It's difficult to do. Therefore, when setting the current ratio, it is practical to roughly determine the current ratio based on the design value of the acceleration current sensitivity of each actuator, and then make corrections based on actual measurements.

In this example, a leaf spring is used as the elastic support member,
Although a part of the elastic support member is provided with a curved part, any form may be used as long as the part of the elastic support member is configured to locally have compliance in the tracking direction.

〔Effect of the invention〕

As described above, according to the present invention, the optical pickup eliminates the disturbance in the displacement characteristics of the second actuator in the tracking direction caused by tracking by the first actuator, and has stable servo characteristics that faithfully follow up to high frequencies. drive device can be obtained.

[Brief explanation of drawings]

Fig. 1 (al), (b) is a side view and front view showing an embodiment of the present invention, Fig. 2 is a characteristic diagram of an embodiment of the present invention, Fig. 3 +8), (b) is a side view and a front view showing an embodiment of the present invention. FIG. 4 is a diagram showing a conventional example, and FIG. 5 is a characteristic diagram of the conventional example. 2... Lens holder 3... Elastic support member 5... Actuator pace roaring also four (c) return

Claims (1)

[Claims] a first actuator that performs track access and tracking; and a second actuator that is connected to the first actuator by an elastic support member and that is capable of driving an objective lens in the focusing and tracking directions with respect to the first actuator. In an optical pickup having an actuator, a constant current source for driving is provided in each of the first actuator and the second actuator, and the ratio of the driving current of the second actuator and the first actuator is set including the mass of the second actuator. An optical pickup driving device characterized in that the acceleration current sensitivity of the first actuator is set to the acceleration current sensitivity of the second actuator.