JPS6131384Y2 - - Google Patents

Description

[Detailed Description of the Invention] This invention relates to a focus motor for controlling the position of an objective lens in the optical system of an optical video disc player, and particularly relates to a focus motor that prevents abnormal vibrations from occurring.

In an optical video disc player, a recorded information signal and a focus control signal are extracted by irradiating a video disc with a light beam and detecting the reflected light beam. In this case, a focus lens is used to focus a beam of light onto the recording surface of the video disc and irradiate it in a spot. This focus lens is focused by a focus motor that is driven by a focus servo system and moves in a direction perpendicular to the recording surface of the video disc.

FIG. 1 is a sectional view of a main part of an example of a focus motor commonly used in the past. In the figure, reference numeral 1 denotes a pole yoke having an inverted T-shape in cross section, and this pole yoke 1 includes a cylindrical pole part 1a having a through hole 2 in the center, and a pole part 1a having a through hole 2 in the center.
Yoke part 1 extending laterally in an L-shape from the lower end of
It is composed of b. A magnet 3 is provided at the end of the yoke portion 1b, and a plate 5 is fixed onto the magnet 3 so as to form a magnetic gap 4 between it and the pole portion 1a. Therefore, these pole portion 1a, yoke portion 1b, magnet 3 and plate 5 are as follows:
This constitutes a closed magnetic path for forming a magnetic gap 4 around the outer periphery of the pole portion 1a. Reference numeral 6 denotes a focus unit, which moves while being guided by the inner wall of a hole 2 formed in the pole portion 1a, and has a focus lens 7 at its tip, as shown in a perspective view in FIG. lens barrel 8 with
and a non-magnetic bobbin 9 which is fixed to the lens barrel 8 in the shape of an inverted cup and whose skirt portion is inserted into the magnetic gap 4 between the above-mentioned pole portion 1a and the plate 5. There is. A coil 10 is wound around the outer periphery of the bobbin 9, and both ends of the coil 10 are connected to a focus servo system. The focus motor 1 configured as described above is arranged so that the optical axis of the focus lens 7 is perpendicular to the information recording surface of the video disc 11 which is rotating at high speed, and It is configured to move along a straight line passing through the center.

In the focus motor configured in this way, when a focus signal is supplied from the focus servo system to the coil 10 wound around the bobbin 9,
A magnetic flux is generated in the coil 10 by this focus signal. In this case, since the coil 10 is located within the magnetic gap 4, the magnetic flux flowing in the closed magnetic path of the pole portion 1a, the yoke portion 1b, the magnet 3, and the plate 5 and the magnetic flux generated by the coil 10 interact with each other. According to the law, the coil 10 receives a force perpendicular to the magnetic flux within the magnetic gap 4, that is, a force perpendicular to the recording surface of the video disk 11. The magnitude and direction of this force are determined in accordance with the magnitude and polarity of the focus signal supplied to the coil 10. Therefore, when the above-mentioned force is applied to the coil 10, the lens barrel 8 slides on the inner wall of the hole 2 formed in the pole portion 1a, and the focus unit 6
moves, and the focus lens 7 is brought into focus on the recording surface of the video disc 11.

However, in the focus motor with the above configuration, there is some gap in the sliding surface between the inner wall of the pole part and the outer periphery of the lens barrel for the purpose of machining accuracy and reducing sliding resistance. Since the acting force applied to the focus unit 6 is only an axial force, the focus unit 6, which should normally move only in the vertical direction, causes an abnormal vibration in which it vibrates from side to side. As a result, the position of the spot irradiated via the focus lens changes in response to the vibration, which causes disturbance to the tracking servo system and tangential servo system, causing the playback screen to change. Uneven coloring occurs.

Therefore, the purpose of this invention is to prevent the occurrence of abnormal vibrations in the focus unit in the focus motor.

In order to achieve this purpose, this idea
By providing a magnetic material between the magnetic gaps of the focus unit, it is possible to apply a lateral force to the focus unit that crosses its optical axis, thereby pressing the lens tube against the inner wall of the hole. This is what I did. Hereinafter, the focus motor according to this invention will be explained in detail using the drawings.

FIG. 3 is a perspective view of essential parts showing an embodiment of the focus unit constituting the focus motor according to this invention, and the same parts as in FIG. 2 are given the same symbols and detailed explanation thereof is omitted. . In the figure, 12 is a thin plate fixed to a part of the outer peripheral surface of the bobbin 9, and is made of a magnetic material such as iron. Then, the bobbin 9 to which the thin plate 12 is attached
A coil (not shown) for driving the focus unit is wound around the outer periphery of the lens, as in the conventional case.

Focus unit 6 configured in this way
When the focus motor is constructed by setting the focus motor on the ball yoke as in the case of FIG. 1, the thin plate 12 made of a magnetic material will be located within the magnetic gap. In this case, since the thin plate 12 is provided only on a part of the outer circumference of the bobbin 9,
The thin plate 12 is attracted to one of the magnetic poles forming the magnetic gap, and a lateral force acts on the focus unit 6. As a result, the lens barrel 8 constituting the focus unit 6 is always pressed against the inner wall on the thin plate 12 side of the through hole provided in the pole portion and guiding the axial movement of the lens barrel 8. Therefore, even if some gap is created between the inner wall of the through hole and the outer periphery of the lens barrel, the lens barrel is pressed against the inner surface of the through hole in one direction and moves in the axial direction. It is possible to completely prevent the occurrence of abnormal vibrations in any direction.

FIG. 4 is a sectional view of a main part of a focus unit showing another embodiment of the focus motor according to this invention, and the same parts as in FIG. 1 are designated by the same symbols. In the figure, 13 is a disk fixed to the tip of the lens barrel 8, and 14 is a magnetic metal ring fixed inscribed in the outer periphery of the disk 13.
The disk 13 and the metal ring 14 constitute a bobbin, and a coil 10 for driving a focus unit is wound around the circumferential surface of the metal ring 14, as in the conventional case.

When the focus unit 6 configured as described above is assembled into a ball yoke in the same manner as shown in FIG. Even when the metal ring 14 is formed by cutting a cylinder, there will be parts where the metal ring 14 is strongly attracted in a certain direction due to processing and installation tolerances. As a result, focus unit 6
is constantly subjected to a force acting in the lateral direction, and as a result, the lens barrel 8 is pressed in one direction against the inner wall of the hole in the pole portion, thereby preventing abnormal lateral vibration.

In addition, in the above embodiment, only the case where a thin plate of magnetic material is fixed to a part of the bobbin and the case where the skirt portion of the bobbin is made of magnetic material are explained, but this invention is limited to this. Instead, it is sufficient to provide a magnetic body in a portion located between the magnetic gaps of the focus unit so that the distribution of magnetic attraction force in the circumferential direction is unbalanced. Therefore, the same effect can be obtained even if the coil itself is made of a magnetic material and its winding is directional.

As explained above, the focus motor according to this invention has a magnetic material in the part located between the magnetic gears of the focus unit to apply a lateral force to the focus unit and press it against the guide body. Since the focus lens is moved in the axial direction, it has an excellent effect of reliably preventing abnormal vibrations in the lateral direction of the focus unit that supports the focus lens.

[Brief explanation of drawings]

Fig. 1 is a sectional view of the main parts of an example of a conventional focus motor, Fig. 2 is a perspective view of the focus unit shown in Fig. 1, and Fig. 3 is a focus unit used in the focus motor according to this invention. FIG. 4 is a perspective view showing one embodiment, and FIG. 4 is a sectional view of a main part of a focus unit showing another embodiment. 1...Ball yoke, 3...Magnet, 4...
...Magnetic gap, 5...Plate, 6...Focus unit, 7...Focus lens, 8...
Lens tube, 9... Bobbin, 10... Coil, 11
...video disc, 12...thin plate, 13...disk, 14...metal ring.

Claims (1)

[Scope of utility model registration request] A lens barrel that slides in a guide hole formed in a pole yoke, a focus lens fixed in the lens barrel, and a magnetic gap of a magnetic circuit that is wound around a bobbin fixed to the lens barrel. In a focus motor having a focus unit having a coil positioned between the two magnetic poles, the distribution in the circumferential direction of the magnetic attraction force in the semicircular direction is axially symmetrical with respect to the center of the optical axis in the portion of the focus unit located between the magnetic gaps. A focus motor that applies an acting force to the focus unit in a direction that intersects the focus control direction by providing a magnetic material to prevent the focus from moving.