JPS62266736A - light pick up - Google Patents

Abstract

PURPOSE:To smoothly attenuate vibrations of a movable part at the time of access by providing a tracking correction servomechanism which detects the tracking-directional displacement position of the movable part with electric signals from a couple of magneto-electric transducing elements and performs feedback control. CONSTITUTION:A signal indicating the momentary rotary displacement of the movable part 20 is led out a subtracter 41 in the form of the difference between voltages outputted by the magneto-electric transducing elements 17a, 17b and inputted to an adder 37 in negative-phase state through an amplifier 43 to control the vibrations of the movable part 20. Consequently, even large vibrations due to an abrupt stop can be attenuated very speedily. Then, a tracking error signal is subtracted 33 from the signal which is multiplied by a proper coefficient through an amplifier 42 and outputted by the subtracter 41 and indicates the rotary displacement position of the movable part 20 and the difference output is phase-compensated and sent to an adder 37 through an amplifier 36. The movable part 20 is driven 39 with the output of the adder 37, so that a stable tracking correcting servo device 40 operates.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application This invention provides an optical disc that is reciprocated in the radial direction.
This invention relates to improvements in optical pickups that read information recorded on optical discs.

Of course, conventional optical pickups include those shown in FIGS. 9 and 10.

The optical pickup A, which is reciprocated in the radial direction R of the optical disk D by a slider motor (not shown), moves up and down relative to the optical pickup body 10 and a guide shaft 11 protruding from the approximate center of the optical pickup body 10. and a rotatably mounted movable part 20 and force). Movable part 2
The optical pickup main body 10 includes two pairs of magnets 12a and 1 as a driving means for causing the objective lens 21 held at zero to follow the track T of the optical disk D in a focused state.
2b, 13a, 13b are provided, and the movable part 20 is provided with a focus coil 23 and tracking coils 24a, 24b.
is wound. These coils are energized by a focus servo mechanism (not shown) or a tracking servo mechanism (not shown), and the movable part 2 is energized by electromagnetic interaction with the magnet.
0 to move the objective lens 21 in the focusing direction or tracking direction of the optical disc D.

22 is a balancer that maintains balance with the objective lens 21.

By the way, when accessing an optical pickup to a predetermined position by external operation, it is desirable that the access time be shorter. Actions such as stopping are required.

However, as mentioned above, the conventional optical pickup A
, the movable part 20 vibrates as shown by the solid line in FIG. 8 due to operations such as high-speed movement and sudden stopping, and it takes a certain amount of time for the signal reading beam irradiated onto the optical disc D to stabilize. Since reading of signals from the optical disk D cannot be performed immediately after access, it has been a common goal to shorten the access time.

In addition, in optical pickups in which tracking servo is performed by moving only the objective lens in the optical system, the push-pull method, which has the simplest structure and has the highest accuracy, is used as the tracking error detection method for the reasons described below. I couldn't do that.

Tracking error detection using push-pull method.

As shown in FIGS. 11 to 14, a signal reading beam that forms a spot S on the optical disc D by the objective lens 21 is reflected by the optical disc D.

This is done by guiding the semiconductor laser to the light receiving element 31 by a beam splitter 85 provided between the semiconductor laser and the objective lens 21.

Since the pits P provided in the optical disk D diffract the beam, the diffraction image S' formed on the light receiving element 31 includes:
Depending on the positional relationship between the spot S and the pit P, light and dark can be distinguished. Each (a) of FIG. 12 to FIG. 14 shows the positional relationship between the spot S and the pit P, and each (b) of FIG. 14 shows the corresponding diffraction image S'. Figure 12~
In the diagram (b) of the 14th rI4, the shaded area is a dark area, and when the spora I-S and the pit P match, the first
A dark image as shown in FIG. 3(b) is formed.

The light receiving element 31 is divided into two parts along a direction corresponding to the longitudinal direction of the pit P on the diffraction image S'.

The subtracter 32 includes each divided detector 31a.

1. A tracking error signal is generated by subtracting the signal output as the bright/dark division from 31b. J! to this tracking error signal! Then, the spot S is moved in the tracking direction R.

However, if a tracking error is detected and in order to correct it, only the objective lens 21 is moved to the position shown by the broken line in Figure 11, the reflected beam will change its path as shown by the broken line. .

Since the other optical systems are maintained at the same position, the movable part 2
When 0 was in the neutral state, the folded image S', which was tied at the position shown by the dashed line in FIG.
As a result, the tracking error signal output from the subtracter 32 will be shifted as a whole to the position shown by the broken line in FIG. Even if it were, the result would be unevenness including DC offset as shown in FIG. 8, making it impossible to stably operate the movable portion 20.

Because of these problems, it has not been possible to employ the push-pull method as a tracking error detection method for an optical pickup that drives only the objective lens 21.

This invention was made in view of the above problems.
In addition to being able to shorten access time, the push-pull method, which has a simple structure and high accuracy, is adopted as a tracking error detection method even in a type where only the objective lens of the optical system is driven during tracking servo. The purpose is to provide an optical pickup capable of

In order to achieve the above-mentioned object, the present invention has a movable part, in which the magnetic field of the magnet provided in the optical pickup main body is changed from one side to the other as the movable part is displaced in the tracking direction. A pair of magneto-electric transducers are provided that move in the direction of increasing and the other in the direction of decreasing, and the tracking servo mechanism detects the displacement position of the movable part in the tracking direction based on the electrical signals from the pair of magneto-electric transducers. It is characterized by the provision of a tracking correction servo mechanism that applies feedback control.

Earth 1 Since this invention has the above-described configuration, the tracking correction servo mechanism applies feedback control to suppress the vibration of the movable part in the tracking direction during access, and also enables error detection using the push-pull method. It is possible to remove the DC offset included in the tracking error signal output by.

1, the present invention will be explained based on the drawings. Figures 1 to 5
The figure shows one embodiment of the present invention. In the figure, parts or members that are the same or equivalent to the conventional ones are denoted by the same reference numerals, and redundant explanations are omitted.

The optical pickup B includes an optical pickup main body 10 having a substantially rectangular shape in plan, holding an objective lens 21, a movable part 20 movably attached to a guide shaft 11 protruding from the center of the optical pickup main body 10, Two pairs of magnets 12a, 12b, and 13a are provided with the section 20 in between.

+3b and a tracking servo mechanism described later.

The optical pickup main body 10 is provided with an optical path hole 15 in its bottom surface 10a to allow a signal reading beam from a laser element (not shown) to enter the objective lens 21 or to allow a return beam reflected by the optical disk D to pass through. has been done. Furthermore, among the two pairs of magnets that are disposed facing each other with the movable part 20 in between, the focus magnet 12 is disposed along the long side of the optical pickup body 10.
a and 12b, and tracking magnets 13a and 13b are arranged along the shorter sides.

The upper surface of the optical pickup main body IO is covered with a cover 14 provided with an opening 14a that exposes the objective lens 21.

The movable part 20 has a substantially rectangular planar shape with arcuate short sides, and has a shaft hole 20a that shares an axis with the guide shaft 11 in the center. The movable part 20 has a shaft hole 2
It is attached to the optical pickup main body 10 through 0g, and can be moved up and down or rotated with respect to the optical pickup main body 10.
The optical pickup main body 10 is elastically supported by suspenders 16 made of elastic members installed between the optical pickup body 10 and the movable part 20.

An objective lens 21 and a balancer 22 for offsetting an imbalance in the weight distribution of the movable part 20 due to the objective lens 21 are disposed in the movable part 20 at symmetrical positions in the longitudinal direction with the guide shaft 11 in between.

In addition, a focus coil 23 is wound around the side of the movable part 20, and two pairs of tracking coils 2 are arranged to cover the focus coil 23 on the shorter side of the movable part 20.
4a, 24b, 24c, and 24d are provided.

The movable part 20 moves the focus coil 2 according to a signal from the focus servo mechanism or the tracking servo mechanism.
3 and focus magnets 12a and 12b.

Or tracking coils 24a, 24b, 24c
, 24d and the tracking magnets 13a, 13b, the objective lens 21 is moved vertically or rotated in the focusing direction or tracking direction.

The suspenders 16 have the function of holding the movable part 20 in a neutral position when these electromagnetic interactions do not work.

In the movable part 20, as the movable part 20 is displaced in the tracking direction, the magnetic field of the tracking magnet 13b, which is provided in the optical pickup main body lO, is moved in one direction in the direction in which the magnetic field increases and in the other in the direction in which the magnetic field decreases. A square flat Hall element 17a, as a pair of magnetoelectric conversion elements that move to
17b is provided.

Hall element 17a,! 7b is a tracking magnet 1 located at the center of each of the adjacent tracking coils 24c and 24d.
3b, and the applied magnetic field changes when the movable part 20 is displaced in the tracking direction. When a normal magnetic field is applied to the Hall elements 17a and 17b while a constant current is flowing, a potential difference is generated between the output terminals, and the potential difference is proportional to the strength of the magnetic field. In addition, there is a Hall element 17a.

If there is no element that influences the output of the movable portion 17b, the displacement of the movable portion 20 in the tracking direction can be detected by detecting this potential difference.

However, the movable portion 20 is provided with a focus coil 23, tracking coils 24c, 24d, etc., and these coils also generate a magnetic field when energized.

Furthermore, the temperature of the Hall cable 17a also depends on the temperature during use.

i, 1. A change occurs in the output of b, .

Therefore, in this invention, regarding elements other than the magnetic field of the tracking magnet 13b, the respective Hall elements 17a and 17
b is equally affected, and by subtracting the outputs of both, it is possible to extract only the information regarding the magnetic field of the tracking magnet 13b, and thereby the displacement position of the movable part 20 in the tracking direction can be detected. can.

FIG. 4 shows a modification of the above embodiment, in which a pair of Hall elements 17a and 17b are two tracking magnets 13a having the same magnetic field.

The tracking coil 2 faces each end of the coil 13b.
It is provided in the center of 4a and 24d.

Also in this case, if the movable part 20 is displaced in the tracking direction, the magnetic field applied to one of the Hall elements 17a and 17b becomes stronger, and the magnetic field applied to the other becomes weaker. The other functions are the same as those in the above embodiment, so their explanation will be omitted.

FIG. 6 is a block diagram of a tracking servo mechanism that displaces the movable portion 20 in the tracking direction in order to cause the objective lens 21 to follow the track T of the optical disc D. Here, an example is shown in which the push-pull method is adopted as the tracking error detection method.

The tracking servo mechanism is composed of a tracking servo mechanism 30 on the outside of the main road, and a tracking correction servo mechanism 40 located inside thereof that applies feedback control to the tracking servo mechanism. The tracking servo mechanism 30 tracks the track T of the optical disc D.
The tracking correction servo 40 detects the displacement of the movable part 20 in the tracking direction and applies feedback control to attenuate the vibration of the objective lens 21 at the time of access. 2
Correct the track tracking scan of 1.

The Hall elements 7-17a and 17b are connected to a subtracter 41, and the two-divided light receiving element 31 is connected to a subtracter 32 that creates a tracking error using a push-pull method.

The output from the subtracter 41 and the output from the subtracter 32, which have been multiplied by an appropriate coefficient in the amplifier 42, are input to a subtracter 33 which removes the DC offset of the tracking error. This subtracter 33 is connected to an adder 37 via a phase compensation circuit 34, a switch 35, and an amplifier 36. On the other hand, this adder 37 receives the output from the subtracter 41 from the amplifier 4.
3 and are input in opposite phase.

The switch 35 is connected to an access voltage generator 38, and is opened from a normally closed state by a signal from the access voltage generator 38 at the time of an access command. The adder 37 is connected to a driver 39 that drives the movable part 20, and the output of the driver 39 is connected to the tracking coils 24a, 24 of the movable part 20.
b, 24c, and 24d.

Next, the operation will be explained.

When the optical player is operated, in order to access the optical pickup B to a predetermined position, the access voltage generator 38 generates a voltage and the switch 35 is opened in response to an access command. Optical pickup B is optical disc D
The vehicle is accessed at high speed across the track T and suddenly stopped at a predetermined position.

However, if no measures are taken to stabilize the movable part 20, the rotating part 20 will vibrate greatly after a sudden stop, as shown by the solid line in FIG. 8, and it will take a long time to stabilize. In this invention, the vibration of the movable part 20, that is, the signal indicating the rotational displacement position at each moment, is output from the subtracter 41 as a difference between the voltages output from the respective Hall elements 17a and 17b.

This signal is input to the adder 37 in opposite phase via the amplifier 43, and is input to the driver 39 as a signal for controlling the vibration of the movable part 20. In response to this signal from the driver 39, each tracking coil 24a of the movable part 20,
Voltage is applied to 24b, 24c, and 24d, and even large vibrations caused by a sudden stop can be attenuated extremely quickly as shown by the broken line in FIG.

Furthermore, when scanning the track T of the optical disc D, the spot of the signal reading beam may deviate from the track T of the optical disc D. This is detected as a deviation in the above light intensity distribution, and is output from the subtracter 32 as a tracking error signal. However, only by this signal, the movable part 2
If 0 is driven, the tracking error signal will include a DC offset as described above (see FIG. 7), making it impossible to perform stable tracking servo. In the present invention, the signal indicating the rotational displacement position of the movable part 20 outputted from the subtracter 41 multiplied by an appropriate coefficient by the amplifier 42 and the tracking error signal outputted from the subtracter 32 are separated into different signals. A subtracter 33 performs subtraction, and the output of this difference is phase compensated by a phase compensation circuit 34, amplified by an amplifier 36, and inputted to an adder 37. On the other hand, the output from the subtracter 41 is suitably amplified by the amplifier 43 and similarly input to the adder 37. A drive signal is output from the driver 39 based on the result of the adder 37, and the movable part 20 is driven. In this way, by applying feedback control by the tracking correction servo machine [40, the DC offset included in the tracking error signal can be removed (see FIG. 6), and stable tracking servo can be realized.

In addition, here we have only talked about the type of optical pickup that performs tracking servo by rotating the movable part.
The present invention is not limited to this, and can also be applied to an optical pickup of a type in which the movable part slides.

As described above, the optical pickup of the present invention has a movable part that moves in the magnetic field of a magnet provided in the optical pickup body in a direction in which the magnetic field increases as the movable part moves in the tracking direction. A pair of magneto-electric transducers are provided, the other one of which moves in a decreasing direction, and the tracking servo mechanism detects the displacement position of the movable part in the tracking direction based on the electrical signals from the pair of magneto-electric transducers and applies feedback control. Since the configuration includes a tracking correction servo mechanism, it is possible to quickly attenuate the vibration of the movable part that occurs during access, shortening the access time, and it also removes the DC offset included in the tracking error signal, making it possible to reduce the vibration during tracking servo. Even in a type of optical system in which only the objective lens is driven, the push-pull method, which has a simple structure and high accuracy, can be used as a tracking error detection method.

[Brief explanation of the drawing]

1 is a plan view showing an embodiment of an optical pickup according to the present invention, FIG. 2 is a cross-sectional view taken along the line ■-■ in FIG. 1, and FIG. 3 is a cross-sectional view taken along the line ■-■ in FIG. FIG. 4 is a plan view showing a modification of the embodiment shown in FIG. 1, FIG. 5 is a block diagram showing an example of a tracking servo mechanism, FIG. 6 is a diagram showing a tracking error signal, and FIG. 7 is a diagram showing a tracking error signal. A diagram of a tracking error signal including a DC offset, Figure i8 is a diagram to explain vibration attenuation during access, Figure 9 is an explanatory diagram showing the operation of an optical pickup, and Figure 10 is a bottom view of a conventional optical pickup. FIG. 11 is a schematic diagram for explaining tracking error detection using the push-pull method. 12(a), 13(a), and 14(a) are explanatory diagrams showing the positional relationship between spots and bits, and FIG.
b), FIG. 13(b), and FIG. 14(b) are explanatory diagrams showing the division of light and darkness appearing in the diffraction image, and FIG. 15 is a diagram showing the diffraction image appearing on the photodetector during normal track scanning. , FIG. 16 is a diagram similar to FIG. 15 showing a state in which the entire diffraction image is shifted downward due to the movement of the objective lens.

Claims (1)

[Scope of Claims] An optical pickup body that is reciprocated in the radial direction of an optical disk, a movable part that holds an objective lens and is movably supported with respect to the optical pickup body, and a movable part that holds the movable part between them. In the optical pickup, the optical pickup has at least one pair of magnets provided on the optical pickup main body, and a tracking servo mechanism that drives the movable part in the tracking direction to make the objective lens follow the track of the optical disk. A pair of magnetoelectric transducers are provided in the section, and the tracking servo mechanism is provided with a pair of magnetoelectric transducers that move in the magnetic field of the magnet, one in a direction in which the magnetic field increases and the other in a direction in which the magnetic field decreases, as the movable part moves in the tracking direction. The optical pickup further comprises a tracking correction servo mechanism that detects the displacement position of the movable part in the tracking direction based on the electric signals from the pair of magnetoelectric transducers and applies feedback control.