JPS59148152A - Optical information reader - Google Patents

Abstract

PURPOSE:To obtain a miniature optical information reader with high accuracy and easy control by using the magnetic attracting force as a spring. CONSTITUTION:Four magnetic members 12a, 12b- having conical sections in the axial direction and fan-shaped sections in the radius direction are provided at upper and lower sides of the outer circumference of a cylindrical holder 11 unified with an objective lens 6. These magnetic members are set opposite to electromagnets 17a, 17b- having conical and U-shaped sections in the axial direction and in the direction rectangular to said axial direction of an outer cylinder case 16 respectively. The holder 11 is supported magnetically in the air and with no contact with the magnetic adsorbing force used as a spring. Then the holder 11 which is magnetically supported with no contact by the feedback control and via a radius direction displacement sensor 13 and an axial direction displacement sensor 21 is moved in accordance with focus and tracking errors to perform an optical reading action. Thus the attachment of a spring is not needed and the spring transmission function can be easily changed owing to the magnetic adsorbing force used as a spring and with no use of a mechanical spring. This attains a miniature optical information reader with high accuracy and easy control.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention provides an information reading device that can optically read audio information or video information without contact, and can also obtain tracking error signals and focus error signals. Regarding.

BACKGROUND ART Conventionally, information is recorded in the form of bits on a spiral track on an information recording medium. To read information, a reading beam such as a laser beam is focused by an objective lens, the spot is moved on a track and guided to the bit, and the modulated reflected beam is stimulated by a photoelectric conversion element to generate an RF' signal. It has gained. However, when reading information, it is necessary to control the information reading sporatra to follow the track so as not to deviate from it, and to maintain the spot focus accurately. In order to achieve this purpose, a mechanism that can move the objective lens for converging the light beam in response to a tracking error signal and a focus error signal is required, and various proposals have been made in the past. Generally, the voice coil of the speaker is used to drive the objective lens, but it has the following drawbacks.

(1) An elastic body such as a leaf spring is used as a member to support the movable object holding the objective lens, but the installation is complicated. In terms of examples, this is because the key point of the era is miniaturization, and space is limited for installing plate parts, etc. (2) The installation of spring materials depends on the workmanship, and it is difficult to move the movable mechanism. Characteristics change critically. In other words, interference may occur between the displacements in the focus direction and the tracking direction, the damping performance of the spring may be reduced, or secondary vibrations may be generated in unexpected places. A reading device with uniform characteristics with small variations cannot be manufactured at low cost.

(3) Once an elastic member such as a reciprocating spring is determined, the characteristics of the movable mechanism are fixed, so if some defect is discovered and a design change is desired, there is no ability to respond.

OBJECTS OF THE INVENTION The present invention provides a novel optical information reading device that overcomes the above-mentioned drawbacks.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will now be described in accordance with embodiments and with reference to the drawings.

FIG. 1 is a configuration diagram showing an embodiment of an information reading device of the present invention. In the figure, the beam emitted from the semiconductor laser (1) is transmitted through the diffraction grating (2), the beam splitter (
3), collimating lens (4), 1/4 wavelength plate (5),
The light passes through an objective lens (6) and is irradiated onto a disk (7) which is an information recording medium. The reflected beam modulated by the bits on the signal surface of the disk (7) passes through the objective lens (
6) Guide the beam downward through the 1 beam splitter (3
) is separated from the incident light by the n1 cylindrical lens (8
) and is guided to the light receiving element (9).

The objective lens (0 is fixed to a holder (O), and the holder 110 is connected to the cylindrical holder 0 with screws or adhesive.The outer periphery of the cylindrical holder α has the same cross-sectional shape in the axial direction. A conical magnetic member (1
2] are arranged in the same radial plane at opposite positions and above and below the axis. Furthermore, a radial displacement sensor for measuring the radial displacement of the movable object including the objective lens (6) is located between the magnetic members (t2 (L) and (1:l) arranged above and below in the axial direction). The magnetic member (14) that is the target of (13) is arranged. Cr5) is the winding coil of the radial displacement sensor (13), which captures the original inductance change when the movable object is displaced in the radial direction. In addition, the outer cylinder case (16) has a nine electromagnet (17eL) whose axial cross section is conical and whose cross section perpendicular to the axial direction is U-shaped.
, (17b) are magnetic members (12α), (12b)
*(19iz), C19b) is a wire-wound coil attached to each of the electromagnets C1'ta], (17b), which are placed opposite to each other with a certain gap (18) between them. (20) is a target for the axial displacement sensor (21) fixed to the lower surface of the cylindrical holder (11).The axial displacement sensor (21) is attached to the fixed plate (22). be.

The gist of the present invention is that the electromagnet winding coil (19,a) e
Using the magnetic attraction force generated by passing a current through the objective lens (19b), the entire movable object is moved between the radial displacement sensor (13) and the axial displacement sensor (5). 21) The movable object is magnetically supported in the air without contact according to the signal obtained from n, and the movable object is moved in a fixed direction while maintaining the contactless state according to the focus error signal and the tracking error signal. In other words, the entire movable object is first magnetically supported at a fixed position by the cap (18) based on the signals from the radial displacement sensor (13) and the axial displacement sensor (21). Although a circuit is required,
When a focus error signal and a tracking error signal are introduced into this servo circuit as target value inputs, the movable object moves in a predetermined direction, making it possible to read information.

The reason why the axial cross-sectional shape of the electromagnet (17α), Cx7b) and the magnetic members (12a), (12b) which are the magnets thereof is conical will be explained. Winding coil of electromagnet with this shape (1'Jz), (19b)
When a current is passed through, a magnetic attraction force is generated in the axial direction and the radial direction perpendicular to the axis, so there is no need to newly provide an electromagnet for axial magnetic support.Next,
The servo circuit shown in FIG. 1 will be explained.

Since the magnetic attraction force is a negative spring force, it constitutes an unstable system in terms of control engineering, but it can be stabilized by performing phase lead compensation. In other words, movable objects can be magnetically supported without contact. FIG. 2 shows a configuration diagram of the servo circuit of the information reading device according to the present invention. In FIG. 1, (23) is the position detection circuit of the radial displacement sensor (13); The electrical output signal is an integral circuit (24) for improving the steady-state characteristics of the servo system.
be guided by. The next stage (25) is a phase lead compensation circuit inserted to achieve stability of the servo system, and its output signal is used to drive a push-pull power amplifier (26 (L),
(26b) and supplies current to the winding coil (19) to magnetically support the movable object at the equilibrium point position.
For example, when the movable object is on the right side of the equilibrium point position in the drawing shown in Figure 1', the radial displacement sensor (1
3) senses f'L and supplies current to the electromagnetic winding coils (19α) and (19b) located at the upper and lower positions on the left side to attract the movable object to the left, so that it is magnetically supported at the equilibrium point. The signal flow explained above is the main loop of the servo circuit, but here the integrator circuit (24)
Consider the case where a certain electrical signal is applied additively.

Since this input is the target value input to the servo circuit, the movable object maintains its magnetic support'! Well, it will move in response to the target value input. Therefore, if the output signal of the tracking error detector [27] is used as the target value input, the movable object including the objective lens [6] will follow the track while maintaining the magnetically supported state (non-contact state). It can be done.

Movement of a movable object in the axial direction, that is, in the focus direction,
The mechanism is similar to that described above. Axial displacement sensor (
The signal from the position detector [28] for 21) is processed by the integrator circuit (29) and the phase lead compensation circuit (?, 0), and the next-stage bushing and pull power amplifier (26) e is excited to move in the axial direction. (31) is a focus error detector, and when this electric signal is added to the integrator (29), the objective lens (31) is moved in the focus direction according to the output signal of (31). However, as you can see from the shape of the electromagnet (17), magnetic attraction is generated in the radial and axial directions when a current is applied.Therefore, control to eliminate mutual interference is relatively difficult. Although difficult, it is possible to suppress this n by devising the circuit of the push-pull power amplifier (26).

As described above, according to the present invention, magnetic attraction force is used as a spring, so it is different from conventional information reading devices that use elastic bodies such as plate springs to support movable objects including objective lenses. Comparatively speaking, it is easy to see if the size can be reduced. This is because the space for storing elastic bodies such as leaf springs can be saved. In addition, since it is not necessary to attach a leaf spring, etc., there is no need to glue the leaf spring or tighten screws (therefore, it has the advantage of simplifying the assembly work.Furthermore, it is possible to increase or decrease the current supplied to the winding coil). In other words, it is possible to change the spring constant by increasing or decreasing the magnetic flux density of the gap [18]. Therefore, it is possible to arbitrarily control the frequency characteristics (transfer function) regarding the displacement of the reader 9-, and it is possible to change the spring constant by increasing or decreasing the magnetic flux density of the gap [18]. It is possible to provide an information reading device with excellent responsiveness.In the conventional information reading device, when sub-resonance or a sharp resonance condition (insufficient damping) occurs in the transfer characteristics related to displacement, the material of the leaf spring, The above problems could only be addressed by changing the shape and mounting or making minor adjustments.In the information reading device according to the present invention, since the spring constant can be changed electrically to some extent, the transfer characteristics If there is a problem such as sub-resonance or insufficient braking, the correction work becomes easy.

[Brief explanation of drawings]

FIG. 1 is a longitudinal sectional view of an optical information reading device showing an embodiment of the present invention, and FIG. 2 is a configuration diagram of a servo circuit. 60. Objective lens, 90. Light receiving element, 10. , holder, 11°0 cylindrical holder, 121. Magnetic member, 13,
radial displacement sensor, 140. Target magnetic member, 1
511 winding coil, 171. Electromagnet, 18°, gap, 19, , electromagnet winding coil, 1. target,
21. , axial displacement sensor. Above 11- Figure 1 Figure 2

Claims (1)

[Claims] On the outer periphery of the cylindrical holder that fixed the objective lens system, magnetic members with a conical cross-section in the axial direction and a sector-shaped cross-section orthogonal to the axis are placed at opposing positions within the same radial plane and in the vertical direction of the axis. A total of four electromagnets are provided, and an electromagnet having a conical cross-section in the axial direction and a U-shape in cross-section orthogonal to the axis is provided at a position facing the magnetic member with a certain gap therebetween,
An optical information reading device comprising radial displacement detection means and axial displacement detection means for a movable object including the objective lens.