Lens forming metal mold, lens forming method and pickup device

A metal mold including: a first inner metal mold which forms a first lens surface and a first flat surface portion of a lens; a first outer metal mold which forms a second flat surface portion; a second inner metal mold which forms a second lens surface and a third flat surface portion; and a second outer metal mold which forms a fourth flat surface portion, and wherein a first protruded portion which forms a first concaved portion on the lens is formed all around an outer periphery of the first inner metal mold, the first concaved portion serving as clearance for a burr, and a second protruded portion which forms a second concaved portion on the lens is formed all around an outer periphery of the second inner metal mold, the second concaved portion serving as clearance for a burr.

TECHNICAL FIELD

The present invention relates to a lens forming metal mold, a lens forming method, and a pickup device.

BACKGROUND

An optical disc drive for reading information from an optical disk, such as CD or DVD, has a pickup device. The pickup device includes at least one laser light source and a lens for focusing a laser light beam emitted from the laser light source on an optical disk.

In general, the lens is a resin molded product formed by mold injection. One example of metal molds for forming a lens is shown in Japanese Patent Provisional Publication No. 2008-126611 (hereafter, referred to as a patent document 1). In order to adjust thickness of the lens, as the metal mold for forming the lens, it is preferable to use an inner metal mold for mainly forming lens surfaces of the lens in combination with an outer metal mold for forming a periphery of the lens.

With the lens of the above-described configuration, since a boundary of the inner metal mold and the outer metal mold is positioned at the periphery of the lens, there is some possibility that burrs occur at the periphery of the lens. On the periphery of one of the lens surfaces (positioned on a side of the laser light source, when the lens is attached to the pickup device) of the lens, a mounting surface for mounting the lens to a lens holder of the pickup device is formed. Since the burrs and the lens holder interfere with each other, the mounting surface cannot be accurately mounted to the lens holder, without removing the burrs. In addition, a cap for preventing contact of the lens with the optical disk is attached to the periphery of the other one of the lens surfaces (positioned on the side of the optical disk, when the lens is attached to the pickup device) of the lens. However, without removing the burrs, there is some possibility that tips of the burrs are placed closer to a side of the disk. Therefore, it is possible that the optical disk is damaged by contacting with the burrs.

SUMMARY

The present invention is achieved so as to solve the above problems. The present invention is advantageous in that it provides a lens forming metal mold and a lens forming method for forming a lens such that the lens can be accurately attached to a lens holder without removing burrs and such that contact of the lens with an optical disk can be prevented by a cap, and provides a pickup device using the lens.

According to an aspect of the invention, there is provided a metal mold for forming a lens, the lens being made of resin and the lens having a first lens surface and a second lens surface, the second lens surface formed on a reverse side of the first lens surface. The metal mold comprises: a first inner metal mold which forms the first lens surface and a first flat surface portion, the first flat surface portion being formed around an outer periphery of the first lens surface, and the first flat surface portion being a ring-shaped surface perpendicular to an optical axis of the lens; a first outer metal mold which forms a second flat surface portion, the second flat surface portion being formed around an outer periphery of the first flat surface portion and positioned closer to a side of the second lens surface than the first flat surface portion, and the second flat surface portion being a ring-shaped surface perpendicular to the optical axis of the lens; a second inner metal mold which forms the second lens surface and a third flat surface portion, the third flat surface portion being formed around an outer periphery of the second lens surface, and the third flat surface portion being a ring-shaped surface perpendicular to the optical axis of the lens, and a second outer metal mold which forms a fourth flat surface portion, the fourth flat surface portion being formed around an outer periphery of the third flat surface portion and positioned closer to a side of the first lens surface than the third flat surface portion, and the fourth flat surface portion being a ring-shaped surface perpendicular to the optical axis of the lens. In this configuration, a first protruded portion which forms a first concaved portion on the lens is formed all around an outer periphery of the first inner metal mold, the first concaved portion serving as clearance for a burr which can occur at a boundary of the first outer metal mold and the first inner metal mold when the lens is formed. A second protruded portion which forms a second concaved portion on the lens is formed all around an outer periphery of the second inner metal mold, the second concaved portion serving as clearance for a burr which can occur at a boundary between the second outer metal mold and the second inner metal mold when the lens is formed.

In the metal mold of the above configuration, the first protruded portion and the second protruded portion are formed so as to form the concaved portions serving as clearance for the burrs between the first outer metal mold and the first inner metal mold, and between the second outer metal mold and the second inner metal mold, namely, at positions where burrs can occur. Therefore, the burr occurs on a position shifted toward the side of the second lens surface from the position of the first flat surface portion, corresponding to an amount of the first concaved portion. The first flat surface portion is used as a mounting surface. Hence, heights of tips of the burr at the side of the first lens surface from the second surface portion are regulated to be low. Thus the tips of the burr do not protrude from the first flat surface portion. Therefore, even if the burr is not removed, the burr does not interfere with the lens holder and it can be ensured that the first flat surface portion, which is the mounting surface, is mounted to the lens holder of the pickup device. Similarly, the height of the burr formed at a side of the second lens surface from the fourth surface portion is regulated to be low by the second concaved portion formed by the second protruded portion formed on the second inner metal mold. Thus, even if the burr is not removed, positions of the tips of the burr at the side of the second lens surface are lower than position of a cap attached to the lens. Hence, the optical disk is not damaged by the burr.

In at least one aspect, the first protruded portion formed around the first inner metal mold may be formed such that a position on the first protruded portion formed around the first inner metal mold approaches to the second lens surface of the lens as the position on the first protruded portion separates from the optical axis of the lens. The second protruded portion formed around the second inner metal mold may be formed such that a position on the second protruded portion formed around the second inner metal mold approaches to the first lens surface of the lens as the position on the second protruded portion separates from the optical axis of the lens.

In at least one aspect, a hole formed in the first outer metal mold for accommodating the first inner metal mold therein and a hole formed in the second outer metal mold for accommodating the second inner metal mold therein may be circular holes having same diameters. Each of the circular holes is formed to have a center equal to a position of the optical axis of the lens.

With such a configuration, both of the hole of the first outer metal mold and the hole of the second outer metal mold can be formed at the same time by overlapping the first outer metal mold and the second outer metal mold and punching them with a drill. Therefore a cost for manufacturing the metal mold is reduced.

According to another aspect of the invention, there is provided a lens forming method, comprising: forming a lens injecting a molten resin material into one of the above described metal molds.

According to another aspect of the invention, there is provided a pickup device, comprising: a lens formed with the above described lens forming method; and a lens holder for holding the lens at the first flat surface portion.

In at least one aspect, the pickup device may further include a cap for covering the fourth flat surface portion of the lens.

As described above, according to the present invention, a lens forming metal mold and a method of fainting a lens such that the lens can be mounted accurately to a lens holder without removing buns, and such that contact of the lens with an optical disk is prevented with a cap, and a pickup device using the lens can be realized.

DETAILED DESCRIPTION OF EMBODIMENTS

Hereinafter, an embodiment of the present invention is explained using figures.FIG. 1is a sectional view of a lens and a pickup device of the embodiment. The pickup device100of the embodiment is a device for reading out data recorded on an optical disk, or for recording data on an optical disk. The lens1is fixed to a lens holder110inside of the pickup device100.

As shown inFIG. 1, the lens1is a lens such that a first lens surface R1is formed on one of its surfaces (the lower side in the figure) and a second lens surface R2is formed on the other one of its surfaces (the upper side in the figure). Both of the first lens surface R1and the second lens surface R2are convex surfaces, and the lens1functions as a convex lens.

The pickup device100causes a laser beam from a laser source to enter the lens1, and irradiates an optical disk with the laser beam collected by the lens1. When data recorded on an optical disk is read out, a laser beam reflects on the optical disk, subsequently, the laser beam enters a photodetector of the pickup device100through the lens1. Namely, the laser beam reflects on the optical disk is eventually read by the photodetector. Here, the laser source and the photodetector of the pickup device100are placed on the side of the first lens surface R1, and, on the other hand, the optical disk is placed on the side of the second lens surface R2.

It is preferable that a distance between the lens1(the second lens surface R2) and the optical disk is short, namely, it is preferable to set a focal length to an infinitesimal length, so as to ensure that data is read out from the optical disk, or so as to ensure that data is recorded on the optical disk. In the embodiment, an optical power of the lens is enlarged by setting a convexity of the first lens surface R1to a large convexity (namely, by setting a radius of curvature of the first lens surface R1to a small length). Therefore, a position of a focal point of the lens1is in close proximity to the second lens surface R2.

The lens holder110is a base for supporting the lens1on the side of the first lens surface R1. As shown inFIG. 1, around an outer circumference of the first lens surface R1of the lens1, a mounting surface11(a first flat surface portion), which is a ring-shaped surface perpendicular to an optical axis AX of the lens1, is formed. Further, on the lens holder110, a holding surface111, which contacts with the mounting surface11of the lens1, is formed. The lens1is fixed on the holder110by placing the mounting surface11of the lens1on the holding surface111of the lens holder110and, subsequently, injecting an adhesive Ab into a corner12of the mounting surface of the lens1.

As described, the optical disk is in close proximity to the second lens surface R2of the lens1. Further, a cap40made with soft resin is attached at a corner22of the lens1so as not to damage the optical disk by contacting the optical disk rotating at a high speed with the corner22at the side of the second lens surface R2of the lens1. When the cap40is attached to the lens1, an upper surface41of the cap40is placed at a higher position than the position of the surface of the second lens surface R2of the lens1(namely, closer to the optical disk). Therefore, even if the optical disk is inclined to the second lens surface R2of the lens1, the optical disk does not contact with the lens1.

Further, a surface for detecting inclination21(a third flat surface portion) which is a ring-shaped surface perpendicular to the optical axis AX of the lens1is formed around a periphery of the second lens surface R2. During attachment of the lens1to the lens holder110, it can be detected whether the lens1is inclined with respect to the lens holder110based on an angle of reflected light by irradiating a laser beam to the surface for detecting inclination21. An inclination of the lens1is adjusted based on a result of the above detection.

Next, a lens forming metal mold of the lens1and a method of forming a lens using the metal mold are explained. In this embodiment, the lens1is made of a plastic, and the lens1is formed by mold injection. A sectional view of the lens1and the metal mold for forming the lens1are shown inFIG. 2.

As shown inFIG. 2, the metal mold200includes an upper metal mold portion210and a lower metal mold portion220. The upper metal mold portion210includes an outer metal mold (up)211and an inner metal mold (up)212. The outer metal mold (up)211has a hole211a, and the inner metal mold (up)212is formed such that the inner metal mold (up)212is placed inside the hole211aof the outer metal mold (up). Additionally, the lower metal mold portion220includes an outer metal mold (down)221and an inner metal mold (down)222. The outer metal mold (down)221has a hole221a, and the inner metal mold (down)222is formed such that the inner metal mold (down)222is placed inside the hole221aof the outer metal mold (down)221. Both of a lower surface211bof the outer metal mold (up)211and an upper surface221bof the outer metal mold (down)221are surfaces perpendicular to the optical axis AX of the lens1. The outer metal mold (up)211is held on the outer metal mold (down)221through contacting the lower surface211bof the outer metal mold (up)211with the upper surface221bof the outer metal mold (down)221.

A concaved portion212afor forming the first lens surface R1of the lens1and a planer portion212bfor forming the mounting surface11are formed with the inner metal mold (up)212. Further, a concaved portion222afor forming the second lens surface R2of the lens1and a planer portion222bfor forming the surface for detecting inclination21are formed with the inner meal mold (down)222.

In the embodiment, the inner metal mold (up)212is movable with respect to the outer metal mold (up)211along the direction of the optical axis AX of the lens1. Similarly, the inner metal mold (down)222is movable with respect to the outer metal mold (down)221along the direction of the optical axis AX of the lens1. The lenses1with various thicknesses can be formed by moving the inner metal mold (up)212and the inner metal mold (down)222along the direction of the optical axis AX of the lens1.

Further, both of an inner circumferential surface of the hole211aof the outer metal mold (up)211and an inner circumferential surface of the hole221aof the outer metal mold (down)221are placed on a same cylindrical surface centered by the optical axis AX. With such a configuration, both of the holes211aand221acan be formed at the same time by overlapping the outer metal mold (up)211and the outer metal mold (down)221and punching them with a drill. And, the inner circumferential surfaces of the holes211aand221abecome concentric cylindrical surfaces with extreme precision by mirror surface finishing of the hole211aand221awhile the outer metal mold (up)211and the outer metal mold (down)211are overlapped. In this manner, since the holes211aand221aare concentrically formed with extreme precision, the inner metal mold (up)212and the inner metal mold (down)222are positioned with high accuracy by the holes211aand221ain a state where the inner metal mold (up)212is attached to the hole211aand the inner metal mold (down)222is attached to the hole221a. And, the concaved portion212aof the inner metal mold (up)212and the concaved portion222aof the inner metal mold (down)222are assembled to the outer metal mold (up)211and the outer metal mold (down)221, respectively, without eccentricity. Consequently, the formed lens1becomes a lens such that an optical axis of the first lens surface R1coincides with an optical axis of the second lens surface R2with extreme precision.

In the embodiment, as described above, the metal mold200is formed by assembling the outer metal molds and inner metal molds. Therefore, when the lens1is formed by injecting a resin into an inside of the metal mold200, the resin flows into a gap between the outer metal mold (up)211and the inner metal mold (up)212and a gap between the outer metal mold (down)221and the inner metal mold (down)222, and burrs occur on the lens1.

In the embodiment, heights of the burrs are regulated so as to prevent the burrs from protruding from the mounting surface11and the surface for detecting inclination21. A configuration of the metal molds for regulating the heights of the burrs is explained below.

FIG. 3is a magnified sectional view corresponding to a dashed line circle portion ofFIG. 2of the lens1and the metal mold200. In the embodiment, a first outer circumferential surface portion13(a second flat surface portion) is formed as a ring-shaped surface, around the outer circumference of the mounting surface11. Further, a second outer circumferential surface portion23(a fourth flat surface portion) is formed as a ring-shaped surface, around the outer circumference of the surface for detecting inclination21. Both the first outer circumferential surface portion13and the second outer circumferential surface portion23are surfaces which are perpendicular to the optical axis AX (FIG. 1) of the lens1. Further, as shown inFIG. 2, the first outer circumferential surface portion13is placed closer to the side of the second lens surface R2(downward in the figure) than the mounting surface11. Similarly, the second outer circumferential surface23is placed closer to the side of the first lens surface R1(upward in the figure) than the surface for detecting inclination21. This is for ensuring the molten resin to pervade the whole of the inside of the metal mold200, when the lens1is formed. Therefore, a first cylindrical surface14is formed between the mounting surface11and the first outer circumferential surface portion and the second cylindrical surface24is formed between the surface for detecting inclination21and the second outer circumferential surface portion, respectively.

As shown inFIG. 2, the first cylindrical surface14is formed by the hole211aof the outer metal mold (up)211, and the second cylindrical surface24is formed by the hole221aof the outer metal mold (down)221. Further, the first outer circumferential surface portion13is formed by an outer circumferential surface portion forming surface211c, which is a surface perpendicular to the optical axis AX (FIG. 2). Furthermore, the second outer circumferential surface portion23is formed by the upper surface221bof the outer metal mold (down)221. As described above, the metal mold200is formed with the outer metal mold (up)211, the inner metal mold (up)212, the outer metal mold (down)221, and the inner metal mold (down)222. Therefore, burrs MF1and MF2, which can be formed, when the lens1is formed, at the sides of the first lens surface R1and the second lens surface R2, respectively, are formed on extension surfaces of the first cylindrical surface14and the second cylindrical surface24, which are respective joints of the molds, respectively, as shown inFIG. 3.

In the embodiment, a protruded portion212chaving a taper surface is formed all over the circumference around the outer periphery of the inner metal mold (up)212(namely, a portion neighboring to the hole211aof the outer metal mold (up)211), the taper surface being such that a point on the taper surface becomes closer to the second lens surface R2as the point becomes farther from the optical axis AX of the lens1. Similarly, a protruded portion222chaving a taper surface is formed all over the circumference around the outer periphery of the inner metal mold (down)222(namely, a portion neighboring to the hole221aof the outer metal mold (down)221), the taper surface being such that a point on the taper surface becomes closer to the first lens surface R1as the point becomes farther from the optical axis AX of the lens1. Therefore, since the above protruded portions212cand222care formed around the outer peripheries of the inner metal mold (up)212and the inner metal mold (down)222, a first concaved portion15and a second concaved portion25, corresponding to the protruded portions212cand222c, respectively, are formed at a corner portion between the first cylindrical surface14and the mounting surface11and at a corner between the second cylindrical surface24and the surface for detecting inclination21, respectively.

In the embodiment, the first concaved portion15and the second concaved portion25, which can be clearance for the burrs, are formed at the positions where the burrs MF1and MF2can be formed. Therefore, the burr MF1occurs at a position shifted toward the side of the second lens surface R2(FIG. 1) from the position of the mounting surface11, corresponding to an amount of the first concaved portion15. Therefore, heights of tips of the burr MF1from the first outer circumferential surface portion13are regulated to be low. Thus the tips of the burr MF1do not protrude from the mounting surface11. Hence, even if the burr MF1is not removed, it can be ensured that the mounting surface11contacts with the holding surface111(FIG. 1) of the lens holder110. Further, the burr MF2occurs at a position shifted toward the side of the first lens surface R1(FIG. 1) from the position of the surface for detecting inclination21, corresponding to an amount of the second concaved portion25. Therefore, heights of tips of the burr MF2from the second circumferential surface portion23are regulated to be low. Thus the tips of the burr MF2do not protrude from the surface for detecting inclination21. Hence, even if the burr MF2is not removed, positions of the tips of the burr MF2are lower than position of the upper surface41of the cap40(FIG. 1).

Further, in the embodiment, the protruded portion212cand the protruded portion222chave the above taper surfaces, but the present invention is not limited to these shapes. An effect of the present invention can be achieved by protruded portions which are merely steep protrusions. However, the protruded portions212cand222cof the embodiment has advantages such that a lens can be easily detached from a mold when punching out after forming the lens, or, production requirements for manufacturing the metal mold200are less.

Additionally, in the embodiment, the mounting surface11, the surface for detecting inclination21, the first outer circumferential surface13and the second outer circumferential surface23are ring-shaped surfaces. However, these surfaces are not necessarily ring-shaped surfaces, but they can be circular surfaces of different shapes.

This application claims priority of Japanese Patent Application No. P2010-049046, filed on Mar. 5, 2010. The entire subject matter of the applications is incorporated herein by reference.