JPS61192039A - Rotary actuator - Google Patents

Abstract

PURPOSE:To obtain a rotary actuator which has the satisfactory frequency characteristics even with the size and the weight approximately equal to a conventional one, by using the ceramics to a holding part for an objective lens which can turn round a rotary center shaft and also can slide in its axial direction. CONSTITUTION:This actuator has the same structure as a conventional one and a material having >=30,000kgf/mm<2> Young's modulus is used to a holding barrel for an objective lens. Here it is required that the specific gravity of said new material is equivalent to that of aluminum. Thus the ceramics of alumina (Al2O3) satisfies those conditions and therefore the objective lens holding barrel uses the ceramics containing >=90% alumina. Furthermore, the side plate part of said lens holding barrel also uses the nonconductive ceramics. This eliminates a phase delay that is produced by an eddy current and secures the satisfactory frequency characteristics.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a rotary actuator used in a pickup for recording and reproducing various optical discs such as optical video discs, compact digital audio discs, and still image disc files. It is.

2. Description of the Related Art Rotary actuators used in compact disc players and the like have generally been constructed as shown in FIGS. 1 to 3.

The configuration and operation will be briefly explained below.

Reference numeral 1 denotes an objective lens holding cylinder made of ceramic, and a top plate 12 made of aluminum, for example, is mounted inside the cylinder. Top plate 12
An objective lens 2 is provided at a position eccentric from the central axis of rotation. Reference numeral 3 denotes a supporting shaft that stands perpendicularly to the yoke 5, and a bearing provided inside the center of the top plate 12 is connected to the part 4. The objective lens holding cylinder performs a tracking operation by rotating around this support shaft 3, and a focusing operation by sliding in the axial direction.

A magnetic circuit for performing this focusing operation and tracking operation will be explained. A ring-shaped magnet 6 is attached to the outer periphery of the yoke 6, and the outer yoke γ is placed on top of the ring-shaped magnet 6.
is installed. The outer yoke 7 consists of a yoke wall 7a and a notch 7b, which are divided into two 90' sections in the circumferential direction and provided at symmetrical positions. The yoke 5 similarly includes a yoke wall 6a and a notch 6b, and the yoke 6 and the outer yoke 7 are arranged such that the yoke walls and the notches face each other. Yoke wall 6a and magnet 6
, a magnetic circuit 8 is formed between the yoke walls 71L, and the outer peripheral portion of the objective lens holding cylinder 1 fits between the magnetic gap 11 between the yoke walls 5a and 7&.

A focusing coil 9 and a tracking coil 10 are mounted on the outer periphery of the objective lens holding cylinder 1.

The focusing coil 9 is wound in the circumferential direction, and when a current is applied to the coil, a force is applied to the coil in the direction of the rotation center axis. controls the movement of the camera and performs focusing. The tracking coil 1o is wound in a rectangular shape and is mounted on the circumference of the objective lens holding cylinder. This tracking coil 1o is composed of coils 10a and 1ob wound in the rotation center axis direction, and coil 10C210d wound in the circumferential direction, and half of the tracking coil 10 has a magnetic air gap. 11, and the remaining half belongs between the notches 6b and 7b. When current is passed through the coils, currents flow in opposite directions in the circumferential direction in the coils 100 and 10d, so they receive forces in opposite directions from each other by the magnetic circuit 8, so the forces cancel each other out. The coil 1o2L in the magnetic gap 1'l receives a circumferential force from the magnetic circuit 8. Coil 10b has a current flowing in the opposite direction to that of coil 101L and receives a force in the opposite direction, so it is disposed in a notch where magnetic circuit 8 is not provided. Generally tracking coil 1o
4 pieces are installed in almost symmetrical positions, each with the same coil □
The direction of the current is considered so that the force is applied in the same direction.

In this way, the tracking operation is performed by controlling the rotation of the objective lens holding cylinder 1 about the central axis of rotation depending on the direction and magnitude of the current flowing through the tracking coil 1o.

Problems to be Solved by the Invention However, the above configuration has the following points of illumination.

For example, in the case of a rotary actuator used in a compact disc player, the objective lens holding tube 1
is generally made of aluminum and measures 15 mm in diameter.
The length of the side plate is about 7 to 8 ff, and the thickness of the top plate is about 3 ff.

However, the objective lens holding cylinder 1 of such a size
, the natural frequency of the holding cylinder 1 itself is 5~e KH
z, and a large sub-resonance occurs around 6 to 6 KHz in the frequency characteristics of the actuator, as shown in FIG. Although the effects of this sub-resonance can be avoided to some extent by using a phase compensation circuit or the like during playback of compact discs, it becomes a major problem in optical discs such as video discs and data files. In general, for optical discs that have a higher rotational speed and a larger disc size than compact discs, the frequency characteristics of actuators used for recording, playback, etc., include sub-resonance and phase 111flf (,
It is required that there be no large sub-resonance at 15 KHzl.

One method of increasing the sub-resonance frequency is to reduce the size of the objective lens holding cylinder 1. FIG. 7 shows the relationship between the field diameter of the objective lens holding cylinder and the sub-resonant frequency. As is clear from the figure, even if the diameter of the objective lens holding cylinder 1 is halved, the resonant frequency increases by only about 5Q%, and the current e KHz becomes about 9 KHz. Furthermore, since the objective lens 2 and the bearing 4 are actually attached to the objective lens holding cylinder 1, it is difficult to reduce its diameter by half.

Another method for increasing the resonance frequency is to increase the thickness of each part of the objective lens holding cylinder 1 to increase its rigidity. FIG. 8 shows the relationship between the thickness of the top plate portion of the objective lens holding cylinder and the sub-resonant frequency. As is clear from the figure, even if the thickness of the top plate is doubled, the resonant frequency is slightly less than twice that, or 10 KH.
It only goes up around z. In addition, doubling the thickness of the top plate almost doubles the weight of the objective lens holding tube 1, which results in a significant decrease in acceleration during focusing and tracking operations. The exterior size of the pickup is also large, which contradicts the pickup development issues of small size and light weight.

As described above, it is extremely difficult to improve the frequency characteristics of conventional rotary actuators without significantly changing their external shape or weight.

SUMMARY OF THE INVENTION In view of the above-mentioned problems, it is an object of the present invention to provide a rotary actuator that has good frequency characteristics while having the same size and weight as conventional actuators.

Means for Solving the Problems In order to solve the above problems, the rotary actuator of the present invention is rotatable around a central rotation axis and slidable in the axial direction of the central rotation axis. The objective lens holder is made of ceramic.

Effects According to the present invention, since the objective lens holder is made of ceramic as described above, the rigidity is extremely high, and the sub-resonant frequency can be increased with the same external dimensions and weight as conventional ones. It is possible to obtain extremely good frequency characteristics.

Embodiment The rotary actuator according to the present invention has a structure of first to
Although it is similar to the one shown in Fig. 3, it is characterized by the material that constitutes the objective lens holding cylinder.

FIG. 4 shows the relationship between the Young's modulus of the material constituting the objective lens holding cylinder and the sub-resonant frequency. If the holding cylinder is made of aluminum, for example, as in the conventional example, the Young's modulus of aluminum is a2ooKyf/ltd, so from FIG. 4, the resonance frequency is 6. a KHz. On the other hand, when the Young's modulus is aoooooKpf/-, the subresonant frequency is approximately 1oxxz
, 3soooKyf/- is approximately 11.2KHz.

Therefore, the objective lens holding cylinder may be made of a material having a Young's modulus of 30oO0Ky f /- or more.

However, in this case, the specific gravity of the material must be comparable to that of aluminum. Metal materials such as iron and titanium have a Young's modulus of less than 30,000 Kff/- and a large specific gravity, making them inappropriate.

Alumina C 120 is a material that satisfies the conditions of
There are 3) ceramics. FIG. 6 shows an example of the relationship between the Young's modulus of alumina. It can be seen that the subresonant frequency is approximately 10 KHz or more when the alumina is 90% or more. Also,
The specific gravity of these ceramics is about 3.0 to 3.5, which is slightly larger than that of aluminum, which is 2.7.

By constructing the objective lens holding cylinder from ceramic containing 90% alumina or more, it has the excellent effect of increasing the sub-resonance frequency to 10 KH2 or more with the same external shape and weight as conventional lenses. .

In addition to the above effects, this embodiment also has the following advantages. In conventional objective lens holding tubes, the side plate of the holding tube, which is a conductor, moves within the magnetic field, so eddy currents are generated in the side plate, which causes a phase delay n in frequency characteristics from KHz or higher. It had a point. In this embodiment, since the side plate portion of the objective lens holding tube is also made of non-conductive ceramic, no phase delay occurs due to eddy currents, and good frequency characteristics can be obtained.

Although this embodiment has been explained using alumina ceramic as an example, the material is not limited to this, and it goes without saying that any ceramic with a small specific gravity and a large Young's modulus will have exactly the same effect. .

Effects of the Invention As described above, according to the rotary actuator of the present invention, the objective lens holder that is rotatable around the rotation center axis and slidable in the axial direction of the rotation center axis is made of ceramic. With this structure, it is possible to obtain a sufficiently high sub-resonant frequency and good frequency characteristics without phase lag.

[Brief explanation of the drawing]

Figure 1 is a perspective view of a general rotary actuator, Figure 2
The figure is a cross-sectional view in the winter direction, and Figure 3 is a cross-sectional view in the Y direction.
Figure 4 is a characteristic diagram of the Young's modulus and sub-resonant frequency of the material used for the objective lens holding tube of the rotary actuator.
The figure is a characteristic diagram of alumina content and Young's modulus, Figure 6 is a frequency characteristic diagram of a conventional rotary actuator, Figure 7 is a characteristic diagram of its objective lens holding cylinder diameter and sub-resonant frequency, and Figure 8 is a characteristic diagram of the thickness of the top plate of the holding cylinder and the resonance frequency. 1... Objective lens holding tube, 2... Objective lens, 3... Support shaft, 4... Bearing,
6, 7... Yoke, 6... Magnet, 8... Magnetic circuit, 9... Focusing coil, IQ... Tracking coil. Name of agent: Patent attorney Toshio Nakao
1 Figure f 1 Objective Shin χ I Silk Compensation Dog T Lid L”is・,j,?=knee yoke---Magnet 9---7 Oh deshinrkozutum 10-) Lapki>')' Figure 2 Figure 2 - Shakuto Figure 3 Figure 41!1 Figure 5 Figure 6 Grade for t% Figure 8

Claims (2)

[Claims] (1) An objective lens holding tube that is rotatable around a rotational center axis and slidable in the axial direction of the rotational center axis, and a position of the objective lens holding tube that is eccentric from the rotational center axis. The objective lens provided in the second part and the objective lens holding cylinder provided in the second part
1. A rotary actuator comprising means for driving in an axial direction, wherein the objective lens holding cylinder is made of ceramic. (2) The rotary actuator according to claim 1, wherein the objective lens holding cylinder is made of ceramic containing 90% or more of Al_2O_3.