JPS5965941A - Objective lens driving device - Google Patents

Abstract

PURPOSE:To prevent a loss of quantity of light, and to make a titled device small-sized and inexpensive, by making an objective lens of an optical head displaceable only in the focusing direction, providing an optical path converting means on an axis of the tracking control direction, fixing a driving rod to the objective lens, and using a piezoelectric element, etc. as a driving source of both of adjusting control. CONSTITUTION:Focus control is executed by applying the control voltage from a focus error detecting part which is not shown in the figure to an electrode of a bend type piezoelectric element 20, and displacing the element 20 in the control direction. Also, minute tracking adjusting control is executed by flowing a control current from a tracking error detecting part which is not shown in the figure to an electromagnetic coil 28, and displacing an optical head outside frame 16 in the control direction to an optical head outside housing 22 through a spherical body 23 by a magnetic force operation of a magnet 29. In case of the tracking control, an incident position of a laser beam to an objective lens 14 is not varied, therefore, a loss of quantity of light is small. The beam always passes through the center part of the objective lens 14, therefore, a lens which scarcely causes aberration to the circumferential part is not required. Also, since the beam is converted by 90 deg. by a prism 18, dimensions in the focus control direction can be made small.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to optical video discs and optical audio discs in which information recorded spirally or concentrically on a recording medium is read by focusing light from a semiconductor laser onto a minute spot using an objective lens. The present invention relates to a drive device for an objective lens in an optical head of an optical head of a disk memory device.

A schematic diagram of a conventional objective lens driving device (2) of this type is shown in FIGS. 1 and 2. In the figure, (2) is the recording medium (1
), an objective lens that focuses the laser beam onto the recording surface of the
(3) is a lens frame that holds the objective lens (2); (4)
is an outer frame, (5) is a leaf spring that holds the lens C) on the outer frame (4), and (6) is an electromagnetic coil attached to the lens frame (6).

(7) is a magnet fixed to the outer frame (4). (8) shows a galpa mirror, and Fig. 2 shows another conventional example. (9) through the objective lens (
2) A pair of leaf springs holding (11), (12)
are an electromagnetic coil and a magnet for controlling the movement of the objective lens (2) in the direction of the tracking adjustment control axis.

Such a conventional objective lens driving device drives the recording medium (1)
Focus adjustment to focus the laser beam into a minute spot on the recording surface is performed using a control current from a focus error detection section (not shown).
The current flows through the electromagnetic coil (6), and the electromagnetic coil (6) and the magnet (
This is done by interlocking the objective lens (2) in the vertical direction in the figure, what is called the focus adjustment control direction, by means of magnetic force with the object lens (7). In addition, although the rough control of dragging is performed by position control eA WQ (not shown), minor control is performed by rotating the galvanomirror (8) in FIG. 1 by means of a control current from a tracking error detection section (not shown). In Fig. 2, the lightning causes a control current to flow through the magnetic coil (11) and the magnetic force between the electromagnetic coil (11) and the magnet (12) causes the objective lens to move in the left and right direction in the figure. This is done by moving in the tracking adjustment control direction. Therefore, if the position control mechanism is used to operate the pickup device at high speed, or if the pickup device is subjected to two external vibrational shocks, unnecessary vibrations will occur in the galvanometer (8) or the objective lens (2). If this vibration can be sufficiently controlled within the control range of focus adjustment control and tracking adjustment control, there will be no problem. It had the disadvantage that it could not be accessed and would fall off the information track if vibrations or shocks were applied from the outside. Furthermore, when the focused beam spot from the objective lens (2) is irradiated obliquely onto the recording surface, the shape of the returning beam light on the light receiving surface (not shown) is deformed, making it difficult to accurately detect the position on the recording surface. It becomes impossible to trace the information track. This angular accuracy was experimentally determined to be 90°±0. It has been determined that the

The factors that impede the accuracy of the above 9o"o, 5' are:
There are warpage and deformation of the recording medium (1), inclination of the objective lens (2), and mechanical attachment precision between the optical head device and the recording medium (1), and the objective lens (2) is moved in the focusing control direction, that is, in the figure. The objective lens (
Since there is no guarantee that the objective lens (2) will move accurately in the direction perpendicular to the recording surface, and will move slightly tilted, the margin for the tilt of the objective lens (2) will be an even smaller value.

Conventionally, a leaf spring (5) is used to prevent the objective lens from tilting, but since the structure does not prevent the objective lens from tilting, it moves slightly tilted, making accurate position detection difficult. It becomes ff1F and the information track is traced and sown. At this time, there was a drawback that if external vibrations or fLi strikes were applied, the information track would fall off. In addition, in the case of Fig. 2, when the movement is controlled in the tracking adjustment control direction, that is, in the horizontal direction in the figure, the leaf spring (10) and the inner frame (
9) (Since the lens moves in an arc j11! using one point as a fulcrum, the lens tilts more than in the case of FIG. 1, and it also has the disadvantage that it is more likely to deviate from the information track.

Also, when attempting to move the objective lens (2) only in the focus adjustment control direction, the only guarantee that the objective lens (2 ribs) will not wobble laterally in the roughing adjustment control direction, that is, in the horizontal direction in the figure, is simply the leaf spring (5). Since the plate spring (10)
Since is a spring whose purpose is to move in the left and right direction, this lateral vibration is more likely to occur than in FIG. Furthermore, in FIG. 2, tracking fl! J 1M When controlling to move the objective lens (2) in the control direction, the leaf spring (5) tends to vibrate in the vertical direction, and when controlling either focus adjustment control or tracking adjustment control. For example, if the objective lens (2) vibrates in the direction of the tracking adjustment control when four-node control is performed on the focus lens, the tracking mmMj control range will be narrowed by this vibration. There is a drawback that tracking adjustment control cannot be performed accurately when an impact is applied.

On the other hand, when controlling tracking adjustment, objective lens Q)
Since the incident position changes, the objective lens (2) needs to be an expensive one with little aberration even at the periphery, and the diameter of the incident light beam needs to be larger than the aperture of the objective lens (2) by the amount of horizontal translation. However, there were drawbacks such as increased light loss. Furthermore, in order to make the force applied by the leaf spring (5) and the amount of displacement of the spring, so-called restoring force characteristics, linear, the leaf spring has to have a complicated shape, which makes it expensive, and there are many variations in the restoring force characteristics. However, it had the disadvantage that it was difficult to make it smaller.

In order to prevent the above-mentioned drawbacks, the present invention makes it possible to displace the objective lens only in the focus adjustment control direction, and includes 41tdi optical path changing means for changing the optical path of the light beam onto the axis in the Trafkin surface control one-node control direction, and tracking adjustment. To provide an objective lens driving device that can be displaced only in the control direction, has a driving rod fixed to the objective lens, and uses a piezoelectric element or a magnetic circuit to use a point-adding sea bream as a driving source for phase control and tracking adjustment. It is.

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 6 is a front sectional view of an objective lens driving device showing an embodiment of the present invention, and FIG. 4 is a sectional view taken along line AA' in FIG. 6 and viewed from the left side. In Figure 6 (1
4) is an objective lens that focuses the laser beam on the recording surface of the recording medium (13), (15) is a lens frame that holds the objective lens, and (16) is a hollow cylinder that has a through hole (16a) on one side thereof. The outer frame of the shaped optical head.

(17) is a structure with a small coefficient of friction, for example, a sphere, and the lens frame (15) and the outer frame (16) are fitted, and the objective lens (14) is tilted or The tracking 1i is configured to be displaced only in the focus adjustment control direction without causing axis deviation in the 14-node control direction. (1
8) is a prism (or mirror) for optical path conversion that is installed in the outer frame (16), and directs the optical path of the laser beam parallel to the four recording deaf bodies (13) through the through hole (16a). The objective lens (14) is turned in a direction perpendicular to the recording medium (13).
The light is focused on the recording surface of the recording medium (16) through the center of the recording medium (16). (19) is a lens drive rod with one end fixed to the center of the objective lens, (22) is a part of the outer casing of the optical head and has a light transmitting (22a); 2
1) and Fi! ! A structure with a small friction coefficient, such as a sphere (2
6) so that it is displaced only in the tracking 174 node control direction and not in the focus adjustment control direction.

(28) is an electromagnetic coil attached to the outer frame (16);
(29) is a magnet fixed to the outer casing (22); (24)
), (25) are compression coil springs that support displacement in the tracking 174-node control direction, (2<5), (2
7) is a spring holder that holds the compression coil springs (24) and (25) having through holes (26a) and (27a), and the through holes (2'6a) and '(27a) are attached to the outer casing (22). ) is an optical path hole that guides a laser beam parallel to the recording medium (13) to the through hole (16a) of the outer frame (16). This objective lens drive device has the 41i21
As shown in the figure, a bent piezoelectric element (20) that deforms when a voltage is applied is provided, and one end of this piezoelectric element (20) is attached to a piezoelectric element fixture (21) fixed to the bottom surface of the outer frame (16). is fixed to another through hole (16b) of the outer frame (16).
The other end of the lens drive rod (19) is fixed through the lens drive rod (19). FIG. 5 shows an explanatory diagram of the bent piezoelectric element. (20a) in FIG. type piezoelectric element (20
) shows the position IF/ of the bent piezoelectric element (20) as a result of applying an electric field of Ivv to the electrode and bending it.
(20b) shows position 11 of the bent piezoelectric element (20) obtained by applying the electric field Ev in the opposite direction and bending it.

Next, the operation will be explained. The position is roughly controlled by a position control mechanism (not shown), and the parallel laser beam that has passed through a semiconductor laser, lens, etc. (not shown) is transmitted through a hole (22a) in the outer casing (22) of the optical head.

Transparent light (26a), (
27a) and the through hole (16a) of the optical head outer frame (16)
The light is reflected at right angles by the prism (18), passes through the center of the objective lens (14), and is focused onto the recording surface of the recording medium (1). Here, the corner point adjustment control is performed at a focal point 5 (not shown).
This is done by applying a control voltage from the prefectural difference detection section to the electrode of the bending type piezoelectric element (20), and displacing the piezoelectric element (20) in the control direction of the W19 node. Further, minute tracking adjustment control is performed by passing a control current from a tracking error detection section (not shown) through an electromagnetic coil (28), and controlling the optical head 1 by the magnetic force formed by the electromagnetic coil (28) and magnet T29.
The frame C6) is positioned at λ in the tracking adjustment control direction with respect to the outside of the optical head t=jf (22) via a sphere (26) with a small friction coefficient. Here the lens frame (15)
and the outer frame (16), for example, a sphere (17) with a small coefficient of friction.
), the objective lens does not tilt, or is displaced only in the vertical direction in the figure without axis deviation or lateral vibration in the tracking adjustment control direction, etc.
The tracking adjustment control direction is also between the outer frame (16) and the outer case (22).
) is displaced only in the left-right direction in the figure via a sphere (23) having a small friction coefficient, for example.

According to this embodiment, focus adjustment control and tracking RIM
Each fIi'i control is performed independently, and when one is controlled, it does not affect the other, such as unnecessary 4M movement, and the objective lens does not tilt, so the focus and tracking adjustment control range is expanded. , Takatsuji access to the information track on the recording surface is also easy, and 1 jill l is easily accessed from the outside.
t++ Even if you are attacked, it will be difficult to get off the information track.

Tracking Q node control is performed by moving the outer frame (16) in the direction of the parallel light beam, so that the objective lens is at the focal point i.
'J! K ffi'l without displacement in the control direction,
Furthermore, as mentioned above, since the objective lens is not tilted, it is easy to detect the position 1 and 1, making it easier to access high lead (C).

Also, when performing tracking adjustment control, the objective lens (1
4) Since the incident position TFi of the laser beam does not change, there is no loss of light h1. Since the laser beam always passes through the center of the objective lens (14) where there is little aberration, a lens with little aberration is required to reach the periphery. First, an inexpensive lens can be used as an objective lens. In addition, prism (18
), the laser beam is turned 90°, so
The size of the focal point Xli in the control direction can be reduced, and a thin optical head can be provided. Since the objective lens used in this optical head converges parallel laser light to one point, it is only necessary to correct spherical aberration, and at the center of the objective lens, the effective diameter of the lens is approximately 1 /10, even if the laser beam light is blocked, the spherical aberration will be large and the spot diameter of the laser beam converged on one point will not deteriorate. As in this embodiment, the lens effective diameter is located at the center of the objective lens (14). Approximately 1/
Even if a thin metal or resin rod with a diameter of 10 culms is fixed in the focus adjustment control direction, the laser beam spot diameter will not deteriorate, and a bent piezoelectric element for focus adjustment control described below can be attached to the other end. For example, the structure can be simplified.

Focus adjustment control is performed by bending the bendable piezoelectric element (20) to displace the objective lens (14).

The bending type piezoelectric element is driven by an electromagnetic coil and a magnet.
Compared to the above, the L and M constructions are simpler and the elastic member can be removed, so the vibration inherent to the spring as the elastic part I can be reduced, so unnecessary vibrations do not occur. Furthermore, the pressure compared to the magnetic circuit? [j, element is external,'
Both l'l and hI can be made smaller, making it possible to make the entire optical head smaller and lighter.In addition, since the quality of tracking adjustment control [11] can be made smaller, tracking II! , +1 node control is also easy, and the response speed can be increased.

In addition, I+
I use compressed coil springs. One compression coil spring has one opening.
It has an excellent restoring force of 11, as is typical of regular springs, and is simple in shape, so it can be obtained at a low price. As a damper phase that absorbs the vibration specific to the spring, an elastic rubber or compression coil spring is coated with resin.
It can easily achieve its purpose as a damper.

FIG. 6 shows a second embodiment of the invention. In Figure 6, the lens frame (15) and outer frame (16) that were fitted through a sphere (17) with a small coefficient of friction have been replaced with a 7-piece resin with a small coefficient of friction, Teflon resin. .

Alternatively, the shape of the pipe is strongly fitted using a low viscosity oil, etc., and the tracking HR control mechanism is also shaped like a spring holding part (26) and C2 force in the same way as above, and the friction coefficient is These are made by using a small fluorine resin, Teflon resin, or a small viscous oil. Focus adjustment control (15'j (%
The fact that both the F racking adjustment control mechanisms can be made into the same shape improves productivity and improves the structure.
Thus, it is possible to provide an inexpensive objective lens drive 11 device tY.

FIG. 7 shows a third embodiment of the present invention, and this tracking-1, 14-node control 1 μ movement device uses a laminated piezoelectric element (30
) is used. This laminated piezoelectric element (RoO) is made by stacking several dozen or more piezoelectric elements with a thickness of 1 rm1 or less, and utilizing the property that the piezoelectric elements are displaced in the stacked direction by applying a voltage, a tracking error detection unit (not shown) is used. A control voltage of 1 is applied to the piezoelectric element (60), and the piezoelectric element (60) is caused to peel only in the tracking adjustment control direction. The structure is simpler than a drive device consisting of an electromagnetic coil magnet, and since the elastic member can be removed, vibration inherent to the spring as an elastic member is eliminated, making it possible to drive an inexpensive lens that does not cause unnecessary vibrations. #I+9 to i! I can provide it.

FIG. 8 shows a fourth embodiment of the present invention, in which a pipe-shaped spring holding part (26+, (27>) is excluded, and the focus if!4 is shown in FIG.
The wli-controlled pressure 11ε element also has fli) v; mold pressure?
1 (element (31) is used and the structure is I'itil.

The present invention is constructed as described above, and the effective portion of the lens is located at the center of the objective lens (14). l; Approximately 1/10f! I
! Even if a thin rod of metal or resin is fixed in the direction of focus adjustment control, the laser beam spot quality will not deteriorate.Furthermore, if a bent piezoelectric element for focus adjustment control described below is attached to the other end, The structure can be simplified.

Further, focus adjustment control is performed by bending the bendable piezoelectric element C20) to displace the objective lens (14). The bending type piezoelectric element has a simpler structure than the driving device ILT using an electromagnetic coil and a magnet, and the elastic member can be omitted, so it is unnecessary.

No vibration occurs. Furthermore, compared to magnetic circuits, piezoelectric elements can be made smaller in both size and mass, making it possible to make the entire optical head smaller and lighter, as well as reducing the quality of tracking torque control, making tracking adjustment possible. Control is also easy and response speed can be increased.

Furthermore, if a stacked PJI type piezoelectric element is used for the tracking adjustment control drive mechanism, the TFQ structure is simpler than the 11λ displacement mechanism made of electromagnetic field magnets, and it is also possible to eliminate the elastic member. It is possible to provide an inexpensive and compact lens driving device that eliminates vibration inherent to a spring as a member and does not generate unnecessary vibrations.

[Brief explanation of the drawing]

Figures 1 and 2 are cross-sectional views schematically showing conventional separate objective lens drive devices! , FIG. 6 is a front cross-sectional view of an objective lens driving device showing one embodiment of the present invention, and FIG. 4 is A of FIG. 6.
-4 line cross-sectional view, No. 51-1, Q3) is an explanatory diagram of the bent piezoelectric element, and FIGS. 6, 7, and 8 are 2. 6th. 1 fake objective lens showing the 4th example! FIG. 3 is a cross-sectional view of the rllI device i'f. (14)...Objective lens, (15)...Lens quality. (16)...outer frame, (17), (2
3)...Support drawing body (for (0))...Bent type Y, electric element, (18)...Prism. (19)...Lens pl〈Φ11 rod, ( 21)・
...Piezoelectric element removal tool. (2... Outer casing (24), (25)
・Compression coil spring. (28)...'fl,? 1ぢPhil, (29)...
Magnet (30), (loυ...f, 11-layer piezoelectric element. Figure 1 Figure 2 Figure 3 JP-A-59-65941 (6) 4th t21 5th factor km t2I

Claims (2)

[Claims] (1) In an objective lens drive device for an optical head that reads information recorded spirally or concentrically on a recording medium by focusing a light beam onto a minute spot using an objective lens, light that is perpendicular to the recording surface of the recording medium is used. A focus adjustment control drive unit 9 disposed on a road and provided with an objective lens held in a lens frame, an outer frame for sliding the lens frame of the objective lens, and a magnetic circuit for controlling the objective lens in a focus adjustment direction. structure, an optical path converting means for converting the optical path of the light beam onto a tracking adjustment control axis parallel to the recording surface, and the focal point R1! (Tracking the node control drive mechanism W1
a tracking adjustment control drive mechanism equipped with a magnetic circuit that controls the tracking adjustment by moving only in the direction of the nodal control axis; a drive rod is fixed to the objective lens in the direction of the focus adjustment control axis; 1. An objective lens driving device, characterized in that a bending type or laminated type piezoelectric element that is deformed by the application of voltage is attached to one end of the objective lens driving device. (2) The objective lens drive device according to claim 1, wherein the tracking adjustment control drive mechanism is provided with a laminated piezoelectric element that is deformed by application of a voltage.