JPS59154656A - Pickup device - Google Patents

Abstract

PURPOSE:To attain accurate control with a simple construction by assembling incorporatedly an optical system and a photodetector, pivoting on a point of center of gravity to drive the assembly and to attain tracking control and pivoting to drive directly vertically via bearings also so as to attain focus control. CONSTITUTION:An output light from a semiconductor laser 1 passes through a collimator lens 2 and a 1/4-wavelength plate 3, then the direction is changed by a total reflection prism 4, the light is irradiated collectively to an information recording surface on a recording medium 6 by an objective 5, the reflected light from the surface is divided by a beam splitter 7 and led to the photodetector 8. Since these are all assembled in a cylindrical housing 9 and fixed in the shape of horizontal type, the point of center of gravity is obtained easily. Shafts 11, 12 and a bearing 13 formed in channel shape attain stable drivine. The driving section consists of a coil and a magnetic circuit and it is required to drive vertically a pickup main body 10 for the purpose of focus control. The pickup main body 10 is formed cylindrically so as to be turned by utilizing an electromagnetic force of a magnetic circuit comprising a coil 14 fitted to a lower end of the shaft 12, a magnet 15 and yokes 16, 17.

Description

[Detailed Description of the Invention] ・Gu, Technique ID: + MinlJzi> The present invention is a pickup device i”r with a T-style disc neck.
It is related to.

<Background of the Invention> An optical disc playback device uses a disk-shaped recording medium (disk) that is engraved in a spiral pattern to form concave and convex portions (referred to as bits).
, the light beam emitted from the light source is focused and irradiated onto a very small area by a light beam, and the light is received by a modulation effect or a transmitted light detector. Changes in the amount of light are converted into electrical signals (read and reproduce information sound).The pickup device that irradiates the focused light spot and detects information is a He-Ne laser or semiconductor laser. It is composed of a total light source 7, an optical system such as an objective lens, and a photodetector.

In such a pickup device, a disk rotating at high speed picks up!・Always focus the irradiation on a minute spot in the column and irradiate it. There is a need.

Conventionally, a movable part that is moved by a drive mechanism, such as the objective lens part of a pickup device, or the entire pickup device, has a structure that is supported by an elastic body such as rubber or a spring, or a movable part that is moved by a drive mechanism. Even if it is directly driven by electromagnetic force from a coil and magnetic circuit, the structure is such that the entire main part slides horizontally in a straight line for tracking control.

A structure supported by an elastic body becomes a second-order vibration system whose equation of motion is expressed by . Here, m is the mass, c is the resistance, k is the spring constant, x is the displacement, I is the current flowing through the coil, and A is the proportionality constant. The resonance frequency fn of this system is as follows, and the phase changes rapidly from 0° to 180° at this fn.

Therefore, in the case of such a driving method, if fn is small, a large servo gain cannot be achieved and oscillation is likely to occur. Furthermore, vibration terms of second order or higher are generally included in many cases, and multiple resonance points of the elastic body appear at frequencies higher than fn, which may prevent sufficient servo gain from being obtained.

In addition, with a structure in which the entire main part slides in a straight line, it requires a large amount of force to slide, and the point where all the force is applied is off the center of gravity, causing rotational force and the area of contact is large, making it difficult to control accurately. This is difficult and has the disadvantage that the structure including the drive mechanism is extremely complicated.

<Object of the Invention> The present invention is based on the fact that the pickup device can be miniaturized by using a semiconductor laser or the like as a light source. By fully supporting the center point and rotating it around its small center, we perform jig control, and by directly driving the entire shaft in the 1ζ direction as well, we perform jig control. It has a simple structure, does not use an elastic body, and can be controlled accurately.

<Example> An embodiment of the present invention will be fully described below with reference to the drawings.

Fig. 1 is a plan view showing one embodiment, and Fig. 2 is A-A in Fig. 1.
3 is a sectional view taken along line A and FIG. 3 is a sectional view taken along line BB in FIG. 1.

As shown in FIG. 2, the output light from the semiconductor laser 1 passes through a collimating lens 2 and a quarter-wave plate 3, and then changes its direction with a total reflection prism 4, and then passes through an objective lens 5.
The information recording surface of the recording medium 6 is irradiated with focused light, and the reflected light therefrom is split by a beam splitter 7 and guided to a photodetector 8.

All of these optical components are assembled and fixed in a cylindrical housing 9. The unit main body 10 has a horizontally elongated structure, and the objective lens 5, photodetector 8, etc. are also arranged on the upper part of the cylindrical body, so that the center of gravity can be easily determined.

The shafts 11, 12 and the U-shaped bearing 13 (see Fig. 3) are constructed separately.The shafts 11, 12 are passed through the U-shaped bearing 13, and then the shafts 11, 12 are inserted. are aligned with the center of gravity at the top and bottom of the unit body 10, respectively, and attached using adhesive or the like. This structure facilitates assembly (adjustments such as axis alignment are also required) and stabilizes the drive described later. In addition, the shafts 11, 1 attached to the upper and lower
The outer periphery of 2 is coated with a material with a low coefficient of friction and finished with high precision. The upper and lower holes of the bearing 13 are drilled with high coaxiality (for example, 5 μm), and the inner surface is polished to make it easier to slide. Furthermore, the outer diameters of the upper and lower shafts 11 and 12 and the hole diameter of the bearing 13 are dimensioned to have very little play and allow for smooth movement.

The drive unit that moves the pickup main body 10, which is stably supported by the bearing 13, consists of a coil and a magnetic circuit. First, in order to perform focus control, it is necessary to drive the pickup main body 10 up and down. This consists of a coil 14 attached to the lower end of the lower shaft 12 and a magnet 1 as shown in FIG.
5. The electromagnetic force generated by the magnetic circuit consisting of yokes 16 and 17 is utilized. These need to be circular so that the pickup main body 10 can also rotate.

On the other hand, track control is performed by rotating (swinging) the pickup body 10 around its center of gravity, and as shown in FIG. It uses electromagnetic force generated by a magnetic circuit. This magnetic circuit has a structure in which magnets 19 and 19 are arranged on both sides to strengthen the force, and is fixed to the bottom plate 21. Although not shown, the bottom plate 21 is placed on a slider portion of an optical disc device and is moved over the entire track range of the disc.

In this way, the pickup main body 10 can perform vertical movement and rotational movement independently, and two-dimensional drive is possible.

Figures 4 and 5 show measurements of the frequency characteristics of the pickup device of this example. Figure 4 is the focus characteristic (vertical movement), and Figure 5 is the radial characteristic (swing movement).
It is. In each case, (a) is the phase characteristic, (
b) shows the amplitude characteristics.

The phase represents the deviation (delay) of vibration relative to the input signal applied to the coil, and the amplitude represents the magnitude of vibration relative to the magnitude of the input signal. In each figure, solid line 2
2, 24, 26, and 28 are the measurement results for this example, and for reference, the measurement results for the case of supporting with a conventional elastic body are shown by the dashed line 2:3°25.27.29. There is.

In a support method that does not use an elastic body, such as the pick-a-nozo neck attachment in this example, the equation of motion is 1 (
Expressed as knee 0. As can be seen from the characteristic diagrams in FIGS. 4 and 5, this yarn has smooth phase characteristics and no multiple resonances, so the servo gain can be larger than when using the elastic body described above.

Furthermore, the reproducibility of characteristics is also high. Also, since tracking control is performed by rotation around the center of gravity, it can be driven with less force than a system in which the entire body moves linearly. Furthermore, a single U-shaped bearing or the like is used to support both vertical and rotational movements, and the area of the contact portion can be made extremely small.

Other features of this embodiment include: (1) By using a semiconductor laser as a light source, it is possible to reduce the size and weight, thereby making it possible to drive the entire device.

(2) The pickup body, which incorporates the light source, etc., is made horizontally long, and the structure is such that shafts can be attached above and below the center of gravity.

(3) The shafts attached to the top and bottom of the lens barrel have a U-shaped integral structure (if the top and bottom bearings are separate and attached later with adhesive, etc., adjustments such as alignment of the legs will be required during assembly) By supporting it with bearings, assembly was facilitated and the drive was stabilized.

(4) The outer periphery of the upper and lower shafts is coated with a material with a low coefficient of friction to improve sliding.

(5) A drive unit using a magnetic circuit that independently performs linear motion and rotational motion can be easily constructed.

<Effects of the Invention> As described above, according to the present invention, it is possible to provide a pickup device that can be driven directly without using an elastic body, has improved frequency characteristics, and facilitates servo control. Further, it is useful because it has many advantages such as a simple structure, a small area of the direct part, and easy driving by electromagnetic force.

[Brief explanation of the drawing]

Fig. 1 is a plan view showing one embodiment of the present invention, and Fig. 2 is a plan view showing an embodiment of the present invention.
Figures 1 and 3 are sectional views taken along the line BB in Figure 1, Figures 4 (a) and (b) are phase and amplitude characteristic diagrams in vertical motion, Figure 5 ( a) and (b) are phase and amplitude characteristic diagrams in rotational motion. 6... Disc, 9... Cylindrical housing, 10...
・Pickup body, 11, 12...shaft, 13...
U-shaped bearing, 14/18...Coil, 15/19...
...Magnet, 16, 17, 23...Yoke. Agent Jr. Physician Fukuju Yoshihiko (and 2 others) No. 71) 1 6 1----------□F2--,・enter 5 A71007 131 Otsuj@I:#/zノtσ no toiooix Tube 5 fights ♂' ((Hz) (b) 10100 / 1 x 1 powder / Hz Norf 101091 to the heart 1 ku ((H!) (b) Sa, 5 (octopus) Continuing from page 1 Hayashi Inventor Mitsuo Ishii 22-22 Nagaike-cho, Abeno-ku, Osaka-shi + j-Sharp Co., Ltd. Inventor Takaaki Okamoto 22-22 Nagaike-cho, Abeno-ku, Osaka City, Sharp Co., Ltd.

Claims (1)

[Claims] An optical system that detects and reproduces 6 beams emitted from a light source through an optical system to an information recording disk, and detects and reproduces the 9\1 beam from the information recording disk. For the pickup device of a disk device, [1] The light source, optical system, and photodetector are all assembled into a cylindrical housing, and the pickup bodies of the J navel are integrated by supporting the center of gravity fQ + lI + of the pickup body. Rotating around the center of gravity to create a trasogging control 1
7.7 to the first drive machine, and +-, +
A second drive mechanism that drives the main body 'jc, Jl-'I-7 and performs a focal point of 1711 ml+.
A pickup device with all the features of Ifii.