SLIDE ACTUATOR

A slide actuator includes: a fixed member; a movable member movable to the fixed member by a predetermined stroke in a predetermined direction; a plurality of balls interposed between the fixed member and the movable member and configured to movably support the movable member; and paired elastic bodies disposed at both ends of a moving range of each of the balls, each of the elastic bodies being configured to come into contact with the corresponding ball when the balls move with movement of the movable member.

BACKGROUND OF INVENTION

1. Field of the Invention

The present invention relates to a slide actuator that supports a movable member through balls so as to be movable to a fixed member.

2. Description of the Related Art

A slide actuator that holds a moved body (for example, optical device) to a movable member disposed to be slidable to a fixed member, and reciprocates the movable body while maintaining an attitude of the moved body orthogonal to a moving direction has been conventionally known, and is adopted for a well-known voice coil motor (VCM) and the like.

For example, Japanese Patent Application Laid-Open Publication No. H8-29656 discloses a technique that moves a plurality of halls along V-grooves (guide grooves) in an apparatus driving a lens in an optical axis direction by the VCM.

In this case, intervals among the plurality of balls are retained constant by a retainer. For example, in a slide actuator101illustrated inFIG. 8AandFIG. 8B, a movable member103are supported through a plurality of balls105so as to be linearly movable to a fixed member102fixed to an apparatus main body. A retainer104is fixed to a surface of the movable member103facing the fixed member102, and the retainer104includes ball housing portions104aallowing movement of the balls105. In addition, the movable member103includes V-grooves103aguiding the balls105.

As illustrated in a left part ofFIG. 9, when the movable member103linearly moves on the fixed member102in a direction of a void arrow, the balls105move by a moving amount of one-half of a moving amount of the movable member103, by rolling frictions f1and f2with the movable member103and the fixed member102. As illustrated inFIG. 10A, a width W of each of the ball housing portion104ain the moving direction is set to a value at which the balls105do not conic in contact with wall parts104beven when the balls105move following linear reciprocation of the movable member103.

In this case, when disturbance such as vibration is applied from the apparatus main body to the fixed member102, the halls105are gradually easily displaced toward the wall parts104bof the ball housing portions104aas illustrated inFIG. 10B. At this time, for example, when large disturbance acts on the fixed member102as illustrated by a void arrow inFIG. 10Cand the balls105come into contact with the wall parts104bof the ball housing portions104a, sliding frictions f2and f3easily occur between each of the balls105and the fixed member102and between each of the balls105and the corresponding wall part104bof the ball housing portion104a.

SUMMARY OF THE INVENTION

A slide actuator according to an aspect of the present invention includes: a fixed member; a movable member movable to the fixed member by a predetermined stroke in a predetermined direction; a plurality of balls interposed between the fixed member and the movable member and configured to movably support the movable member, each of the balls being disposed in the movable member; and paired elastic bodies disposed at both ends of a moving range of each of the balls, each of the elastic bodies being configured to come into contact with the corresponding ball when the balls move with movement of the movable member.

A lens driving apparatus according to another aspect of the present invention includes: a slide actuator including a fixed member, a movable member movable to the fixed member by a predetermined stroke in a predetermined direction, a plurality of balls interposed between the fixed member and the movable member and configured to movably support the movable member, each of the balls being disposed in the movable member, and paired elastic bodies disposed at both ends of a moving range of each of the balls, each of the elastic bodies being configured to come into contact with the corresponding ball when the balls move with movement of the movable member; a lens; a magnet; and a coil, wherein, the movable member holds the lens, the magnet is fixed to a periphery of the movable member, and the coil is wound around an outer periphery of the fixed member.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Some embodiments of the present invention are described below with reference to drawings. Note that the drawings are schematic, and relationship between a thickness and a width of each member, ratios of thicknesses of respective members, and the like are different from relationship and ratios of actual members. Portions having dimensional relationship and ratios different from one another are included among the drawings as a matter of course.

First Embodiment

FIG. 1toFIG. 6illustrate a first embodiment of the present invention. First, a reference numeral1inFIG. 1denotes an electromagnetic slide actuator. The slide actuator includes a fixed member2fixed to an unillustrated apparatus main body, a movable member3linearly movable on an inner surface2aof the fixed member2by a predetermined stroke Ls, and a plurality of balls5that are interposed between the fixed member2and the movable member3and movably support the movable member3.

The balls5are housed one by one in ball housing portions3aprovided in the movable member3. Although not illustrated, guide grooves (V-grooves) linearly guiding movement of the balls5are provided on the inner surface2aof the fixed member2and surfaces of the ball housing portions3afacing the inner surface2a.

The movable member3holds, for example, an optical device10as a moved body, and a permanent magnet7is fixed to a periphery of the movable member3. In addition, a coil8is disposed at a position separated by a distance where the coil8receives an appropriate magnetic field from the permanent magnet7so as to face an outer periphery of the permanent magnet7. The coil8is wound around an outer periphery of the fixed member2. Note that the slide actuator1according to the present embodiment is of a movable magnet type. However, the slide actuator may be of a movable coil type in which a coil is attached to the movable member3and the permanent magnet faces the coil.

An output side of an actuator control unit11is connected to the coil8through an actuator driving unit12. Further, a position detection sensor13that detects a movement position of the movable member3is connected to an input side of the actuator control unit11.

The actuator control unit11mainly includes a well-known microcomputer including a CPU, a ROM, a RAM, and an interface, each well-known. The actuator control unit11compares actual positional information of the movable member3detected by the position detection sensor13with a movable member instruction value set as a target position, and outputs a control signal to correct a control deviation to the actuator driving unit12.

Then, the actuator driving unit12outputs a driving current corresponding to the control signal to the coil8, and Lorentz force is generated by the magnetic field of the permanent magnet7, which slides the movable member3. A moving direction of the movable member3is determined by a direction of the current applied to the coil8, and magnitude of force of the movable member3is changed by an amount of the current.

For example, when the actuator driving unit12applies the movable member instruction value (driving current) of a sine wave to the coil8in response to a PWM signal outputted from the actuator control unit11, the movable member repeats linear reciprocation in a predetermined direction by the predetermined stroke Ls. In this case, in a case where it is assumed that slippage does not occur between the movable member3and each of the balls5and between each of the balls5and the inner surface2aof the fixed member2, each of the balls5reciprocates following the movable member3by a moving amount of one-half of the moving amount of the movable member3.

Further, free ends6aof a pair of wire springs6as elastic bodies protrude to each of the ball housing portions3a, at both ends of a moving range Lb of each of the balls5. In each of the ball housing portions3a, the free ends6aface a center between the inner surface2aof the fixed member2and an opposing surface of the ball housing portion3awith Which the corresponding ball5come into contact in a diameter direction, and a position of each of the free ends6abecomes a contact point P described below. Therefore, an interval W′ (seeFIG. 5A) between opposing surfaces of the free ends6ais set to at least a value obtained by adding the moving range Lb to the diameter of each of the balls5(seeFIG. 5B), and the free ends6aare disposed at an interval slightly greater than the value.

When each of the balls5comes into contact with the corresponding free end6aat a predetermined pressure or more, the free end6aelastically deforms and buffers the pressure applied from the ball5at the contact point P (seeFIG. 5C). Wall parts3bface the respective free ends6aat a predetermined interval in a deformation direction. The wall parts3bfunction as restriction members for preventing the respective free ends6afrom deforming (plastically deforming) beyond an elastic limit.

FIG. 2andFIG. 3each illustrate a specific shape in a case where the above-described slide actuator1is adopted as a voice coil motor (VCM)1′. The voice coil motor1′ functions as, for example, a lens driving apparatus driving a lens. In the voice coil motor1′, the movable member3holding the lens, etc. is formed in a square cylindrical shape, and the permanent magnet7is attached to each of two opposing surfaces of the movable member3.

The fixed member2supports the movable member3so as to be movable in an optical axis direction, and the fixed member2includes notches allowing movement of the permanent magnets7in an axial direction. Further, the coil8is wound around the outer periphery of the fixed member2within a range wider than a value obtained by adding the moving range to a length of each of the permanent magnets7in the axial direction.

On the other hand, in the movable member3, the ball housing portions3aintegrally provided with the guide grooves are provided at both edge parts in a direction orthogonal to the moving direction (hereinafter, referred to as “short direction”) on a side surface3cof the movable member3.

In the present embodiment, the movable member3are supported by three balls5(three-point supporting). Therefore, the ball housing portions3aare provided at two positions at one of the edge parts and at one position at the other edge part in the short direction of the side surface3c. Further, the two ball housing portions3aprovided at one of the edge parts are provided at symmetrical positions with a center in a direction along movement of the movable member3(hereinafter, referred to as “longitudinal direction”), in between. The ball housing portion3aprovided at the other edge part is provided at the center in the longitudinal direction.

As illustrated inFIG. 2, in the present embodiment, the six wire springs6in total that are disposed one pair by one pair in the ball housing portions3aare held in a cantilever manner by the side surface3cwhile being orthogonal to the moving direction of the movable member3. As illustrated inFIG. 5A, the wire springs6are disposed at equal intervals W′, and each of the wire springs6has, at one end part, the free end6aprotruding to the corresponding ball housing portion3a.

As described above, each of the free ends6aof the wire springs6elastically deforms to buffer impact when the balls5collide with the respective free ends6a. The deformation can reduce generation of sliding frictions of each of the balls5. A spring constant k of each of the free ends6a(substantially, each of wire springs6) is set within a range represented by the following inequality (1).

Although not illustrated, pressure lightly urging each of the balls5against the inner surface2aof the fixed member2is generated in the movable member3in a non-contact state using repulsive force, attraction force, or the like of the magnet.

where x1<x2 is established.

Further, the value Fx is represented by the following equation.

In the equation, Fx is maximum static frictional force generated between the movable member3and the inner surface2aof the fixed member2per one ball5. μ1 is a maximum static friction coefficient between the movable member3and the balls5, μ2 is a maximum static friction coefficient between the balls5and the inner surface2aof the fixed member2, M is a mass of the movable member3, m is a mass of the balls5, g is gravitational acceleration, n is the number of balls5, x1 is a displacement amount of the contact point P between the free end6aof each of the wire springs6and the corresponding ball5generated by the predetermined stroke of the movable member3, and x2 is a displacement amount of the contact point P between the free end6aof each of the wire springs6and the corresponding ball5at the elastic limit of the free end6aof each of the wire springs6.

FIG. 4schematically illustrates action of the force represented by the above-described equation (2). In this case, the mass M of the movable member3includes a mass of the optical device10as the mounted moved body. Further, in a case where the movable member3lightly urges each of the balls5against the inner surface2aof the fixed member2by repulsive force, attraction force, and the like of the magnet, the urging force is included in the mass M, which makes it possible to set the spring constant k with higher accuracy.

According to the inequality (1), in a case where the spring displacement amount x is equal to x1 (x=x1), under a condition that each of the wire springs6is the hardest, the amount of spring force (reaction force) k·x pushing back the corresponding ball5when the spring displacement amount exceeds a predetermined amount even a little, in other words, the amount of spring force k·x not pushing back the corresponding ball when the amount of spring force is within the predetermined amount, is represented as follows.

Further, in a case where the spring displacement amount x is equal to x2 (x=x2), a condition that each of the wire springs6is the softest, in other words, the amount of spring force k·x pushing back the corresponding ball5before the spring displacement amount reaches a plastic region, is represented as follows.

In this case, the free end6aof each of the wire springs6is plastically deformed at x≥x2. Therefore, an actual usable range is x<x2,

In the case where the slide actuator1is the voice coil motor1′, urging force f in a slide direction acts on the movable member3. Therefore, the equation (2) is turned into an equation (2′).

FIG. 6illustrates relationship between the displacement amount x and the amount of spring force k·x of each of the wire springs6in a case where the value Fx determined by the equation (2′) is applied to the inequality (1). The spring constant k is set based on the preset Fx (amount of spring force k·x acts in opposite direction, seeFIG. 4) between the displacement amounts x1 and x2 in an area surrounded by inclinations of linear lines (limit values of spring constant k) at which sliding frictions is not generated in each of the balls5, set by the above-described inequality (1).

For example, as illustrated inFIG. 6, in a case where a vertical axis represents the force Fx acting on each of the balls5, when the spring constant (inclination) k is set within a range between the displacement amounts x1 and x2, the sliding frictions generated in each of the balls5is suppressed. In addition, each of the wire springs6(each of free ends6a) can buffer impact within the elastic deformation range without plastically deforming.

Next, action according to the present embodiment having such a configuration is described. The actuator control unit11compares the actual positional information of the movable member3detected by the position detection sensor13with the movable member instruction value set as the target position, and outputs the control signal to correct the control deviation to the actuator driving unit12. Then, the actuator driving unit12applies the corresponding movable member instruction value (driving current) to the coil8, and linearly reciprocates the movable member3within the range of the stroke Ls.

When the movable member3moves, each of the balls5rotates by the rolling frictions, and reciprocates in the moving range Lb (=Ls/2) of one-half of the stroke L2 as the moving range of the movable member3, following the movable member3. In a case where each of the balls5follows the movement of the movable member3without generating sliding frictions, each of the balls5performs following operation within the moving range surrounded by the free ends6aof the wire springs6protruding to the corresponding ball housing portion3a.

However, when the control deviation of the movable member3is increased, displacement accordingly occurs in each of the balls5, and each of the halls5is displaced in a direction toward the free end6aof one of the corresponding wire springs6as illustrated inFIG. 5B. At this time, when the control deviation of the movable member3is increased due to influence of disturbance and the like, the displacement of each of the balls5is increased, and each of the balls5collide with the free end6aof one of the corresponding wire springs6at the contact point P as illustrated inFIG. 5C. As a result, each of the free ends6aelastically deforms by the pressing force applied to the contact point P, and buffers the impact.

At this time, the spring constant k of each of the wire springs6is set within the range of the inequality (1) based on the preset amount of spring force k·x (seeFIG. 6), which suppresses generation of the sliding frictions of each of the balls5and reduces the control deviation of the movable member3. Further, suppression of the sliding frictions of each of the balls5makes it possible to suppress deterioration of abrasion resistance.

In a case where each of the balls5applies force exceeding the set amount of spring force k·x to the free end6aof one of the corresponding wire springs6, the free end6ais caught by the wall part3bof the corresponding ball housing portion3aand further deformation is restricted. Therefore, the free end6adoes not plastically deform and is not damaged.

As described above, according to the present embodiment, even in the case where each of the wire springs6receives impact from the corresponding ball5, setting the spring constant k of each of the wire springs6within the range of the inequality (1) based on the preset amount of spring force k·x makes it possible to buffer the impact by elastic deformation of the free ends6ain the state where the sliding frictions generated in each of the balls5are suppressed. Further, reducing the sliding frictions generated in the balls5makes it possible to improve durability and to realize prolongation of lifetime.

Note that in the present embodiment, the wire springs6are illustrated and described as elastic bodies; however, the elastic bodies may be plate springs or wire rubbers.

Second Embodiment

FIG. 7illustrates a second embodiment of the present invention. Note that the components same as the components in the first embodiment are denoted by the same reference numerals, and descriptions of the components are simplified or omitted.

In the above-described first embodiment, the wire springs6are adopted as the elastic bodies and are disposed in a cantilever manner in the direction orthogonal to the moving direction of the movable member3. The impact applied from the balls5are buffered by the elastic deformation of the respective free ends6aprovided at the end parts of the wire springs6.

In contrast, in the present embodiment, paired compression springs21facing each other are provided as the elastic bodies in both wall parts3bprovided in each of the ball housing portions3aof the movable member3. A spring constant k of each of the compression springs21is determined from the above-described inequality (1). In addition, a free length of each of the compression springs21from the corresponding wall part3bis set to a length of a position of the free end6aof each of the wire springs6described in the first embodiment. Further, each of the compression springs21at a solid length functions as a restriction member.

In such a configuration, when the movable member3linearly reciprocates within the range of the stroke Ls, each of the balls5reciprocates in the moving range Lb (=Ls/2) of one-half of the moving range of the movable member3, following the movable member3. In the case where each of the balls5follows the movement of the movable member3without generating sliding frictions, each of the balls5performs the following operation between the corresponding both compression springs21, as illustrated inFIG. 7A.

However, when the control deviation of the movable member3is increased, displacement accordingly occurs in each of the balls5, and each of the balls5is displaced in a direction toward one of the corresponding compression springs21as illustrated inFIG. 7B. At this time, when the control deviation of the movable member3is increased due to influence of disturbance and the like, the displacement of each of the balls5is increased, and each of the balls5press one of the corresponding compression springs21at the contact point P as illustrated inFIG. 7C. Note that the positions of the contact points P pressed by the respective balls5are set to the positions same as the positions in the first embodiment.

Then, each of the compression springs21elastically deforms by the pressing force applied to the contact point P, and buffers the impact. At this time, the spring constant k of each of the compression springs21is set within the range of the inequality (1) based on the preset amount of spring force k·x (seeFIG. 6), which suppresses generation of the sliding frictions of each of the balls5and reduces the control deviation of the movable member3. Further, suppression of the sliding frictions of each of the balls5makes it possible to suppress deterioration of abrasion resistance.

In a case where each of the balls5applies force exceeding the set amount of spring force k·x to one of the corresponding compression springs21, the length of each of the compression springs21become the solid length as illustrated inFIG. 7C. Therefore, the further deformation of each of the compression springs21is restricted.

As described above, in the present embodiment, the compression springs21as the elastic bodies are provided on the wall parts3bof each of the ball housing portions3aof the movable member3, and the impact from the balls5are buffered by the elastic deformation of the compression springs21in the state where generation of the sliding frictions is suppressed. Therefore, it is possible to achieve effects similar to the effects by the above-described first embodiment. Further, each of the compression springs21at the solid length functions as the restriction member. This makes it possible to easily set the elastic limit of each of the compression springs21. Note that the elastic bodies are not limited to the compression springs21and may be compression rubbers.