GB2367112A - Spring coupling apparatus used in optical deflection device - Google Patents

Abstract

A spring coupling apparatus is used in an optical deflection device and includes a plurality if spring plates (22), a first coupling part (26<SB>1</SB>) having a plurality of prong elements (26B), a second coupling part (26<SB>2</SB>) having a tubular body (26D) through which the prong elements (26B) of the first coupling part (26<SB>1</SB>) can extend, and urging means for producing relative rotation between the first (26<SB>1</SB>) and second (26<SB>2</SB>) coupling parts when the prong elements of the first coupling part (26<SB>1</SB>) extend through the tubular body (26D) to enable gripping of the spring plates (22) when the plates are located between adjacent prong elements (26B) of the first (26<SB>1</SB>) and second (26<SB>2</SB>) coupling parts.

Description

OPTICAL DEFLECTION DEVICE HAVING

ELECTROMAGNETIC DRIVER ASSEMBLED THEREIN FOR ROTATIONALLY DRIVING OPTICAL DEFLECTION ELEMENT The present invention generally relates to an optical deflection device for deflecting a light beam, such as a laser beam, which is used, for example, as an element of an optical system for recording digital data on and reading the recorded digital data from an optical disk or optical-magnetic disk. The invention relates in particular to such an optical deflection device having an electromagnetic driver assembled therein for rotationally driving an optical deflection element, which deflects a light beam made incident thereon.

As a representative optical deflection device, a galvano-mirror device is well known. The galvano-mirror device comprises a yoke member, a movable member rotatably supported by the yoke member through the intermediary of a pair of resilient elements, an optical deflection element, such as a prism, a mirror or the like, securely attached to the movable member, and an electromagnetic driver for rotationally driving the movable member with respect to the yoke member.

The electromagnetic driver includes a pair of permanent magnets provided on the yoke member, and an electromagnetic coil provided on the movable member and interposed between the permanent magnets. The electromagnetic coil is disposed in a

magnetic field, generated by the pair of permanent magnets, and the movable member, carrying the optical deflection element, is rotated in accordance with Fleming's Rule, when the electromagnetic coil is electrically energized.

In general, there is a demand for the optical deflection device to have a constructional compactness and for the movable member, and therefore the optical deflection element, to exhibit a high-speed drive capability. The high-speed drive capability of the optical deflection element depends upon a product of the magnetic flux density (B) of the magnetic field produced by the permanent magnets, and a wire length (L) of the electromagnetic coil, i. e. BxL. An increase in the magnetic flux density (B) results in a bulkiness of the optical deflection device. Accordingly, the wire length (L) of the electromagnetic coil should be increased in order for the highspeed drive capability of the optical deflection element to be improved.

Nevertheless, the longer the wire length (L) of the electromagnetic coil, the larger the resistance and the selfinductance of the electromagnetic coil. Thus, it is difficult to improve the high-speed drive capability of the optical deflection element by merely extending the wire length (L) of the electromagnetic coil.

Therefore, an object of the present invention is to provide an optical deflection device, having an electromagnetic

driver assembled therein for rotationally driving an optical deflection element, wherein a high-speed drive capability of the optical deflection element can be efficiently and effectively improved without substantially increasing the bulkiness of the optical deflection device.

In accordance with the present invention there is provided an optical deflection device comprising a base member, a movable member having-an-optical deflection element, such as a prism element, a reflective mirror element, a light-beamdeflecting hologram element or the like, a set of resilient support elements at the sides of the movable member and interposed between the base member and the movable member, such that the movable member is resiliently and movably supported by the resilient elements with respect to the base member, and an electromagnetic driver that rotationally drives the movable member with respect to the base member. The electromagnetic driver includes a first set of permanent magnets provided on the base member to produce a first magnetic field, and a second set of permanent magnets provided on the base member to produce a second magnetic field, and the first set of permanent magnets and the second set of permanent magnets are reversed arrangements such that the first magnetic field and the second magnetic field are reversed with respect to each other. The electromagnetic driver further includes a first electromagnetic coil provided on the movable member and disposed in the first

magnetic field, a second electromagnetic coil provided on the movable member and disposed in the second magnetic field, and the respective first and second electromagnetic coils are electrically energized in the first and second magnetic fields in such a manner that electric currents flow through the first and second electromagnetic coils in opposite directions, whereby the respective first and second electromagnetic coils are subjected to rotational-forces in the same rotational direction.

Preferably, the movable member comprises a holder portion for receiving the optical deflection element, resulting. in a simple and compact arrangement of the optical deflection device. In this case, the first and second electromagnetic coils may be symmetrically provided on the holder portion about a vertical plane that includes the center of mass of the holder portion. The holder portion of the movable member may be cylinder-shaped.

Preferably, the permanent magnets in the first set are sector-shaped, and are associated with each other to surround the first electromagnetic coil, and the permanent magnets in the second set are sector-shaped, and are associated with each other to surround the second electromagnetic coil. In this case, the sector-shaped permanent magnets in each set are arranged such that opposite magnetic poles are opposing each other.

So that stable and reliable resilient and movable support of the movable member can be obtained, each of the resilient support elements may comprise a leaf-spring assembly which is formed from a plurality of leaf-spring elements arranged at uniformly angular intervals around an elastic-mainaxis of the movable member.

The elastic-main-axis of the movable member may coincide with an inertial-main-axis of the movable member, to thereby ensure a stable and reliable rotational movement of the movable member. Alternatively, the elastic-main-axis of the movable member may coincide with a thrust-main-axis of the movable member, to thereby ensure a stable and reliable rotation of the movable member. Preferably, the elastic-main-axis of the movable member coincides with both the inertial-main-axis and the thrust-main-axis of the movable member, to thereby obtain a greater stability e and reliability of the movable member's rotational movement. Also, the leaf-spring elements are preferably identical to each other.

The optical deflection device may further comprise a set of releasable couplings, provided at the sides of the movable member, releasably connecting an end of the corresponding leafspring assembly to the movable member, whereby simple and correct mounting of the leaf-spring between the base member and the movable member can be obtained.

By way of example, these objects and other objects of

the present invention will be better understood from the following description, with reference to the accompanying drawings in which: Figure 1 is an exploded perspective view of an optical deflection device embodying the present invention; Figure 2 is an exploded perspective view of a movable member of the optical deflection device shown in Fig. 1; Figure 3 is an exploded perspective view of a leafspring assembly of the optical deflection device shown in Fig.

1; Figure 4 is an exploded perspective view of a coupling for the leaf-spring assembly shown in Fig. 3; Figure 5 is a front view of the coupling of Fig. 4; Figure 6 is a longitudinally-sectioned view of the movable member, showing two electromagnetic coils, provided thereon, together with two sets of sector-shaped permanent magnets associated therewith, as shown in Fig. 1 ; Figure 7 is a schematic view corresponding to Fig. 6, showing the movable member with the two electromagnetic coils, symbolically indicating a direction in which an electric current flows through each of the electromagnetic coils; Figure 8 is a longitudinally-sectioned view similar to Fig. 6, showing a comparative example of the present invention; Figure 9 is a schematic view corresponding to Fig. 8, showing the movable member with the two electromagnetic coils,

symbolically indicating a direction in which an electric current flows through each of the electromagnetic coils ; and Figure 10 is a perspective view of the leaf-spring assembly shown in Fig. 1.

Figure 1 shows an optical deflection device embodying the present invention, which comprises a base member 10 made of a suitable metal, such as aluminum, an aluminum alloy or the like. The base member 10 includes a mounting portion lOA, and a frame portion lOB formed with a circular-opening 10C and unitarily extended vertically from the mounting portion lOA.

During assembly, the mounting portion 10A is used for attaching the optical deflection device to an optical system. When operating, the optical system records digital data on and reads the recorded digital data from an optical disk or opticalmagnetic disk.

The optical deflection device also comprises a movable member 12 having a cylindrical shape. The movable member 12 is constituted as a part of the optical deflection device, and is received in the circular opening 10C of the frame portion lOB in a manner stated in detail hereinafter.

The optical deflection device further comprises a generally-rectangular cover member 14 attached to a front side of the base member 10, and a magnet holder member 16 attached to a rear side of the base member 10. The generally rectangular cover member 14 has a circular opening 14A formed therein. The magnet holder member 16 includes a collar-shaped holder portion 16A, and two lug portions 16B unitarily extending diametrically from sides of the holder portion 16A.

Preferably, the cover member 14 and the magnet holder member 16 may be made of the same metal as that of the base member 10.

Note, the holder portion 16A defines a part of the base member 10, and may be integrally formed with the base member 10, if necessary.

Two sets, in this case, pairs, of sector shaped permanent magnets (181 ; 182 and 201 ; 202) are located in the holder portion 16A, and the permanent magnets (181 ; 182 and 201 ; 202) in each pair are arranged such that opposite magnetic poles are opposing each other in a manner as mentioned in detail hereinafter. Note, in Fig. 1, one (201) of the permanent magnets 201 and 202 is not visible. The lug portions 16B are used for attaching the magnet holder member 16 to the base member 10. The attachment is performed such that the holder portion 16A is accommodated in the circular opening 10C of the frame portion 10B.

As best shown in Fig. 2, the movable member 12 comprises a cylindrical holder portion 12A for receiving a prism element 12B, which serves as an optical deflection element. In this embodiment, another type of optical deflection element, such as a reflective mirror element, a light-beam-deflecting hologram element or the like, may be substituted for the prism element

12B.

The cylindrical holder portion 12A includes a central flange 12A1 having a polygonal shape, two collar elements 12A2 and 12A3 protruding from respective sides of the central flange 12Al'and two electromagnetic coils 12C and 12D mounted on the collar elements 12A2 and 12Ag, respectively. As is apparent from Fig. 2, when the electromagnetic coils 12C and 12D are mounted on the collar elements 12A2 and 12Ag, these coils 12C and 12D are symmetrically positioned on the holder portion 12A about a vertical plane that includes the center of mass of the holder portion 12A, hereinafter referred to as the neutral or rest plane. The electromagnetic coils 12C and 12D operate in conjunction with the two sets of sector shaped permanent magnets (181 ; 182 and 201 ; 202), thereby rotatably driving the movable member 12, and therefore the prism element 12B.

Note, in Fig. 2, although each of the electromagnetic coils 12C and 12D is illustrated as a mere ring element, the coils 12C and 12D are actually formed by turning of a wire into a ring-like shape.

When the optical deflection device is assembled, the sector shaped permanent magnets 181 and 182 are associated with each other so as to surround the electromagnetic coil 12C, and the sector-shaped permanent magnets 201 and 202 are associated with each other so as to surround the electromagnetic coil 12D.

With the present invention, the electromagnetic relationship

between the two pairs of sector shaped permanent magnets (181 ; 182 and 201 ; 202) and the electromagnetic coils 12C and 12D is particularly significant, and will be explained later in detail with reference to Figs. 6 and 7.

The movable member 12 is further provided with two couplings 12E diametrically fixed to the central flange 12Ai.

Each of the couplings 12E includes an immovable coupling part 12E,, and a movable coupling part 12E2 detachably associated therewith. In particular, the central flange 12A1 has two narrow diametrically-opposed side faces, in each of which a threaded hole 12A4 is formed. Each immovable coupling part 12E1 has an integrally-formed screw 13 protruding therefrom, and the screw 13 of the immovable coupling part 12E1 is fixedly threaded in the hole 12A4. Note, in Fig. 2, only one of the couplings 12E is illustrated.

A leaf-spring assembly 22 is connected at its one end to each of the couplings 12E, and is composed of two H-shaped spring plates 23, as shown in Fig. 3. The H-shaped spring plates 23 are identical to each other, and a central slit 24 is longitudinally formed in each spring plate 23, such that two leaf spring elements 22A are defined therein. The leaf-spring assembly 22 is obtained from the two H-shaped spring plates 23 by crosswisely interlinking them via the central slits 24 thereof. Thus, in this embodiment, a leaf-spring assembly 22 is formed from the four leaf spring elements 22A spaced apart

from each other at uniformly angular intervals around a central longitudinal axis of the leaf-spring assembly 22, so as to define an angle of 90 degrees between two contiguous leaf spring elements 22A.

As is apparent from Fig. 2, the other end of the leafspring assembly 22 is connected to another coupling 26, which includes an immovable coupling part 261, and a movable coupling part 262 detachably associated therewith. The coupling 26 is substantially identical to the coupling 12E, except that the immovable coupling part 261 is provided with an integrally formed block element 28 in place of the screw 13 of the

immovable coupling part 12E The block element 28 has a through-hole 28A formed therein, and is used for securely attaching the immovable coupling part 261 to the base member 10.

As best shown in Fig. 4, the immovable coupling part 26 has a castellated element 26A unitarily extending from the block element 28. Four prong elements 26B protrude from the projecting end face of the castellated element 26A. The four prong elements 26B are spaced apart from each other at uniform angular intervals around a central longitudinal axis of the castellated element 26A, so as to define an angle of 90 degrees between the neutral planes of two adjacent prong elements 26B.

Also, the four prong elements 26B are identical to each other, each of the prong elements 26B having a sector shaped cross

section. The castellated element 26A has a pair of flat faces 26C formed thereon, the flat faces 26C being diametrically opposed to each other. Note, in Fig. 4, only one of the flat faces 26C is visible.

The movable coupling part 262 of the coupling 26 comprises a tubular castellated element 26D, a diameter of which is larger than that of the castellated element 26A, enabling the castellated element 26A of the immovable coupling part 261 to be slidably and rotatably received in the tubular castellated element 26D of the movable coupling part 262. The castellated element 26D has four prong elements 26E, the four prong elements 26E being spaced apart from each other at uniformly angular intervals around a central longitudinal axis of the castellated element 26D, so as to define an angle of 90 degrees between the neutral planes of two adjacent prong elements 26E.

Similar to the prong elements 26B of the immovable coupling part 261, the four prong elements 26E are identical to each other, each of the prong elements 26E having a sector shaped cross-section. The castellated element 26D has two pairs of flat faces 26F and 26G formed thereon, and the flat faces (26F, 26G) in each set are diametrically opposed to each other. Each of the flat faces 26F has a threaded hole 26H formed therein, and each of the flat faces 26G has a threaded hole 261 formed therein. Note, in Fig. 4, only one of the flat faces 26F is visible, and only one of the flat faces 26G is visible.

As best shown in Fig. 5, each of the threaded holes 26H and 261 is not positioned at a center of the corresponding flat face (26F, 26G). In particular, the respective threaded holes

(26H, 26I) in each pair are offset from the centers of the corresponding flat faces (26F, 26G) while remaining diametrically opposed.-In-other words, the threaded holes 26H and 261 are arranged so as to be offset from the centers of the flat faces 26F and 26G, respectively, in a counter-clockwise direction in Fig. 5.

Accordingly, after the castellated element 26A of the immovable coupling part 261 is slidably and rotatably received in the tubular castellated element 26D of the movable coupling

part 262, as shown in Fig. 5, two screws 30 (Fig. 4) are threaded in two diametrically-opposed holes (26H or 26I), dependent upon the orientation of the tubular castellated element 26D with respect to the flat faces 26C of the castellated element 26A, until the respective tips of the screws 30 abut the flat faces 26C. The movable coupling part 262 is thereby subjected to a clockwise rotational force, whereby each of the prong elements 26E of the movable coupling part 262 is pressed against the corresponding prong element 26B of the immovable coupling part 261.

Thus, after a crosswise end of the leaf-spring assembly 22 is engaged with the coupling 26, such that the four respective ends of the leaf spring elements 22A are located and clamped between the prong elements 26B and 26E, by threading the screws 30 in the diametrically-opposed holes (26H or 26I), the leaf-spring assembly 22 can be securely connected to the coupling 26.

Note, a secure connection between the coupling 12E and the other crosswise end of-the leaf-spring assembly 22 can be carried out in the same manner as with the coupling 26, because the structure of the coupling 12E is identical to that of the coupling 26, as mentioned above.

As is apparent from Fig. 1, each couplings 26 is securely attached to the frame portion lOB of the base member 10, by inserting a bolt element 32 into the through-hole 28A of the block element 28, and then by threading the bolt element 32 into a corresponding threaded hole 10D formed in the frame portion lOB. The threaded holes 10D are located in two respective diametrically formed recesses in the frame portion 10B, whereby each of the couplings 26 is accommodated in the corresponding recess. Thus, the movable member 12 is supported by the frame portion lOB through the intermediary of a pair of leaf-assemblies 22.

In short, use of the pair of releasable couplings 12E and 26 enables simple and correct mounting of the leaf-spring assemblies 22 between the base member 10 and the movable member

12.

As mentioned above, with the present invention, the sector shaped permanent magnets (181 ; 182 and 201 ; 202) are arranged such that opposite magnetic poles are opposing each other, as shown in Fig. 6. Namely, as is apparent from this

drawing, the inner pole of the permanent magnet 181 is the N pole, whereas the inner pole of the permanent magnet 201 is the S pole. Similarly, the-inner pole of the permanent magnet 182 is the S pole, whereas the inner pole of the permanent magnet 202 is the N pole. In short, the respective magnetic fields, produced by the pairs of sector shaped permanent magnets (181 ;.

182 and 201 ; 202) are reversed with respect to each other.

On the other hand, when the optical deflection device is driven, the respective electromagnetic coils 12C and 12D are electrically energized in the magnetic fields, produced by the two pairs of permanent magnets (181 ; 182 and 201 ; 202), in such a manner that electric currents flow through the electromagnetic coils 12C and 12D in opposing directions, as symbolically shown in Fig. 7. Thus, the electromagnetic coils 12C and 12D are subjected to the rotational forces F in the same direction, in accordance with Fleming's Rule, whereby the movable member 12 is rotated in the rotational direction indicated by the forces F. Of course, the rotational direction of the movable member 12 depends upon a direction in which the electric current flows through each of the electromagnetic

coils 12C and 12D.

With the present invention, during the electrical energization of the electromagnetic coils 12C and 12D, these coils 12C and 12D are not subjected to any mutual inductance, due to the electric currents flowing through the electromagnetic coils 12C and 12D in opposing directions, as shown in Fig. 7. Therefore, it is possible to efficiently and effectively increase the high-speed drive capability of the movable member 12 without an increase in the bulkiness of the optical deflection device.

Figure 8, similar to Fig. 6, shows a comparative example of the present invention. Note, in this drawing, elements identical to those of Fig. 6 are indicated by like references primed. This comparative example is derived from the process of development of the optical deflection device of the present invention.

As shown in Fig. 8, in the comparative example, although the sector-shaped permanent magnets (181' ; 182'and 201' ; 202') in each pair are arranged such that opposite magnetic poles are opposing each other, the inner poles of the permanent magnets 181'and 201'are the same (N), and the inner poles of the permanent magnets 182'and 202'are the same (S). Accordingly,

before the movable member 12A'can be rotated in one of the rotational directions, the respective electromagnetic coils 12C'and 12D'are electrically energized in the magnetic

fields, produced by the two pairs of permanent magnets (18* ; 182'and 201' ; 202'), in such a manner that electric currents flow through the electromagnetic coils 12C'and 12D'in the same direction, as symbolically shown in Fig. 9.

Nevertheless, a mutual inductance is produced in each of the electromagnetic coils 12C'and 12D', and thus it is impossible to efficiently and effectively produce a high-speed drive capability of the-movable member 12A', and consequently, the optical deflection element or prism 12B'.

When the optical deflection device is driven, the movable member 12 is rotated around a central longitudinal axis. of the leaf-spring assemblies 22, because the leaf-spring assemblies 22 exhibit a high compliance around the central longitudinal axis thereof.

In particular, as shown in Fig. 10, when a three dimensional coordinate system is defined with respect to each leaf-spring assembly 22, such that a H-shaped spring plate 23 is included in both the X-Z plane and the Y-Z plane of the coordinate system, and such that the central longitudinal axis of the leaf-spring assembly 22 coincides with the Z-axis of the coordinate system, the compliance (indicated by reference a) around the X-axis of the coordinate system is substantially equal to the compliance (indicated by reference ) around the Y-axis of the coordinate system, which is considerably lower than the compliance (indicated by reference y) around the Z

axis of the coordinate system.

Accordingly, when the movable member 12 is subjected to the rotational forces F, the movable member 12 is rotated around the rotational axis defined by the cental longitudinal axes (Z-axis) of the set of leaf-spring assemblies 22, and is referred to as an elastic main axis of the movable member 12 hereinafter.

Also, as is apparent from the foregoing, since each of the leaf-spring assemblies 22 exhibits a high compliance only around the central longitudinal axis thereof, the leaf-spring assemblies 22 are less susceptible to structure coupled oscillations and thrust coupled oscillations. Note, the structure coupled oscillations are defined as coupled oscillations produced in the leaf-spring assemblies 22 due to outside forces exerted upon the optical deflection device, and the thrust coupled oscillations are defined as coupled oscillations produced in the leaf-spring assemblies 22 due to rotational forces of the movable member 12. In short, the rotational movement of the movable member 12 can be stably and reliably performed.

The arrangement of the mass of the movable member 12 is configured such that the center of mass thereof is located on the rotational axis of the movable member 12. Namely, the elastic main axis (Z-axis) of the movable member 12 can substantially coincide with an inertial main axis of the

movable member 12, which passes through the center of mass thereof. By incorporation of this concept, the production of the structure coupled oscillations can be further suppressed in the leaf-spring assemblies 22.

Furthermore, an arrangement of the mass of the movable member 12 may be configured such that a rotational center thereof is located on the rotational axis of the movable member 12. Namely, the elastic main axis (Z-axis) of the movable member 12 may substantially coincide with a thrust main axis of the movable member 12, which passes through the rotational center thereof. By incorporation of this concept, the production of the thrust coupled oscillations can be further suppressed in the leaf-spring assemblies 22.

Of course, preferably, the elastic main axis, inertial main axis, and thrust main axis of the movable member 12 should coincide with each other, thereby ensuring greater suppression of the structure coupled oscillations and the thrust coupled oscillations in the leaf-spring assemblies 22, resulting in increasingly stable and reliable rotational movement of the movable member 12.

Finally, it will be understood by those skilled in the art that the foregoing description is of a preferred embodiment of the device, and that various changes and modifications may be made to the present invention.

Claims (5)

1. A leaf spring coupling apparatus comprising : a plurality of leaf spring plates extending from an axis and being parallel to and spaced uniformly around the axis; a first coupling part having a plurality of prong elements spaced uniformly about said axis; a second coupling part having a tubular body through which the prong elements of the first coupling part can extend, the second coupling part having a plurality of prong elements spaced uniformly about said axis; and urging means for producing relative rotation between the first and second coupling part when the prong elements of the first coupling part extend through said tubular body to enable gripping of said leaf spring plates when said plates are located between adjacent prong elements of the first and second coupling parts.

2. A leaf spring coupling apparatus according to claim 1 wherein the first and second coupling elements have an identical number of prongs.

3. A leaf spring coupling apparatus according to claim 1 or 2 wherein the number of prongs of the first and second coupling elements correspond to the number of leaf spring plates.

4. A leaf spring coupling apparatus according to any one of claims 1 to 3 wherein the first coupling part including means for fixedly attaching to a base member.

5. A leaf spring coupling apparatus as herein described with reference to the accompanying drawings.