CN110692234B

CN110692234B - Lens actuator having OIS and AF functions

Info

Publication number: CN110692234B
Application number: CN201780091481.3A
Authority: CN
Inventors: 宇野胜; 米山厚司
Original assignee: Huawei Technologies Co Ltd
Current assignee: Huawei Technologies Co Ltd
Priority date: 2017-06-09
Filing date: 2017-06-09
Publication date: 2021-04-09
Anticipated expiration: 2037-06-09
Also published as: WO2018223382A1; CN110692234A

Abstract

The invention provides a lens actuator. The lens actuator includes: a piezoelectric element for moving the lens holder in the optical axis direction; a Shape Memory Alloy (SMA) for moving the lens holder in a predetermined direction perpendicular to the optical axis direction; and a Voice Coil Motor (VCM) for moving the lens holder in a direction perpendicular to the optical axis direction and different from the predetermined direction. The present invention reduces or eliminates the magnetic influence of OIS systems.

Description

Lens actuator having OIS and AF functions

Technical Field

The present invention relates to a lens actuator for an imaging apparatus and having an Optical Image Stabilization (OIS) and an Auto Focus (AF) function.

Background

In a camera, an AF function is used to focus an image to be photographed on an image sensor by moving a lens in an optical axis direction (a direction in which lens centers are aligned), and an OIS function is used to suppress an image from being blurred due to hand shake at the time of photographing by moving the lens in a direction perpendicular to the optical axis.

The OIS system of the camera module is increasingly popular in the smartphone market because by using the OIS system, everyone can take a fine picture even in a dark place or when there is hand shake. On the other hand, the dual-camera system is also increasingly popular in the smartphone market, because applications such as zoom, 3D, and AF control can be implemented by using the dual-camera system. These two trends are likely to converge and therefore a dual OIS system will be required in the near future. The conventional OIS system has a problem of magnetic field leakage due to the moving magnet system. Thus, a breakthrough invention is needed to address this leakage problem. Meanwhile, miniaturization technology is required and reduction of current consumption is also urgently required.

The conventional OIS system has a problem of magnetic field leakage. If dual cameras are used, the actuator next to the OIS actuator must be modified to be a yoke actuator. In this type of actuator, the yoke and the AF magnet are located as far away as possible from the OIS system. In the case of a dual OIS system, the two OIS systems cannot be placed side by side because they can adversely affect each other due to magnetic field leakage.

Disclosure of Invention

The present invention provides a solution for reducing or eliminating the magnetic influence of OIS systems and a unique system that integrates a piezoelectric element, Shape Memory Alloy (SMA) and Voice Coil Motor (VCM). The present invention is a combination of a bump style piezo AF actuator, an SMA OIS for one direction, and a VCM OIS that rolls using the drive shaft of the bump style piezo AF actuator.

The present invention provides a system with a piezo-element system for AF, a movement system for diagonal direction by using SMA wires and a movement system for direction perpendicular to diagonal direction by using VCM for OIS. The invention relates to VCM, SMA and piezoelectric technology. In particular, the actuator module comprises two OIS actuators and one AF actuator on one base. The invention includes piezo-element AF actuators and CSV (combined SMA and VCM) OIS actuators. It is therefore an object of the present invention to provide a dual OIS system without magnetic field leakage. It is another object of the invention to reduce the current consumption of the entire actuator system being used. As a dual camera module system, it is an important object of the present invention to provide high quality images that are merged from two different sensors.

According to a first aspect, there is provided a lens actuator, wherein the lens actuator comprises: a piezoelectric element for moving the lens holder in the optical axis direction; a Shape Memory Alloy (SMA) for moving the lens holder in a predetermined direction perpendicular to the optical axis direction; and a Voice Coil Motor (VCM) for moving the lens holder in a direction perpendicular to the optical axis direction and different from the predetermined direction. In this structure, the influence of the magnetic field can be reduced. In a first possible implementation form of the first aspect, one end of the piezoelectric element is coupled to the driving shaft, the lens holder includes an elastic body and a support structure, and the elastic body pushes the driving shaft toward the support structure. This structure allows the lens holder to move in the optical axis direction and to swing about the drive shaft.

With reference to the first possible implementation manner of the first aspect, in a second possible implementation manner of the first aspect, a waveform for reducing friction between the driveshaft and the support structure and the elastic body is superimposed on a waveform applied to the VCM for correcting hand shake. In this structure, the movement in the optical axis direction can be smoothed.

With reference to the first or second possible implementation manner of the first aspect, in a third possible implementation manner of the first aspect, the other end of the piezoelectric element is coupled to a weight, the weight is coupled to the moving base, and the SMA contracts according to the voltage to be applied and moves the moving base relative to the fixed base. In this configuration, the mobile base can move without the magnet. With reference to the third possible implementation manner of the first aspect, in a fourth possible implementation manner of the first aspect, the lens actuator further includes a guide rail located between the moving base and the fixed base. In this structure, the moving direction can be stabilized.

With reference to the first aspect or the first to fourth possible implementation manners of the first aspect, in a fifth possible implementation manner of the first aspect, a magnet of the VCM is fixed on the lens holder, a coil of the VCM is fixed on the moving base to face the magnet, and the lens actuator includes a magnetic core located behind the coil and having a high magnetic permeability. By using a magnetic core having a high magnetic permeability, magnetic field leakage can be suppressed.

With reference to the fifth possible implementation manner of the first aspect, in a sixth possible implementation manner of the first aspect, the neutral axis of the magnet faces the center of the magnetic core. In this structure, the neutral axis of the magnet is pulled to a position facing the center of the core. In combination with the first aspect or the first to sixth possible implementations of the first aspect, in a seventh possible implementation of the first aspect, there is provided an electronic device including two lens actuators arranged side by side in one plane. In this structure, various dual-camera systems can be realized while reducing the magnetic field leakage.

With reference to the seventh possible implementation manner of the first aspect, in an eighth possible implementation manner of the first aspect, the two lens actuators are placed in different directions, so that a distance between the magnets is larger than a distance when the magnets are placed in the same direction. In this configuration, since the distance between the magnets is long, the influence of the magnetic field can be reduced.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below. It is obvious that the drawings in the following description only show some embodiments of the invention and that other drawings can be derived from them by a person skilled in the art without inventive effort.

Fig. 1 shows a top view of a lens actuator provided by the present invention;

fig. 2 shows a side view of the lens actuator as viewed from the point (a) shown in fig. 1;

fig. 3 shows a cross-sectional view of the groove 18(18a and 18b) and the ball 19 along a chain line from the upper right to the lower left in fig. 1;

fig. 4 shows a cross-sectional view of the groove 22(22a and 22b) and the ball 23 along a chain line from upper left to lower right in fig. 1;

fig. 5 shows the magnetic core 10 and the coil 8 as viewed from the point (B) shown in fig. 1;

fig. 6 shows the magnet 7 at the rear of the core 10 and the coil 8 as viewed from the point (B) shown in fig. 1;

fig. 7 shows the thrust movement of the AF drive engine unit 12;

fig. 8 shows the relationship between the velocity and the incident amount (inclusion) without/with jitter;

FIG. 9 shows an example arrangement of two lens actuators;

fig. 10 shows another example arrangement of two lens actuators.

Detailed Description

The technical solution in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. The described embodiments are only a part, not all, of the embodiments of the invention. All other embodiments, which can be obtained by a person skilled in the art without making creative efforts based on the embodiments of the present invention, belong to the protection scope of the present invention. The invention features novel features. The figures are for illustration purposes only and are not drawn to scale. Moreover, like numerals refer to like features in the drawings. The invention itself, both as to organization and method of operation, may best be understood by reference to the detailed description which follows taken in conjunction with the accompanying drawings.

Fig. 1 shows a top view of a lens actuator provided by the present invention, and fig. 2 shows a side view of the lens actuator as viewed from the point (a) shown in fig. 1. In fig. 2, the stationary base 4 is fixed to, for example, a camera module of a smartphone. The photographic subject is located at the top of fig. 2, and the image sensor is disposed below the stationary base 4. The centers of the movable base 2 and the fixed base 4 are opened enough to transmit the light of the lens to the image sensor.

In fig. 2, the AF drive engine unit 12 includes a drive shaft 121, a piezoelectric element 122, and a weight 123. The wires that supply current to the piezoelectric element 122 are not shown in fig. 2. When current is supplied, the piezoelectric element 122 expands or contracts depending on the direction of the voltage. The AF drive engine unit 12 moves the lens holder 5 upward or downward. The lens holder 5 has a lens barrel 6 therein, and the lens barrel 6 has a plurality of lenses therein.

Referring to fig. 1, one end of the support spring 11 pushes the driving shaft 121 to the V-shaped area of the slider 13(13a and 13b), and the driving shaft 121 is caught by the support spring 11 and the slider 13. That is, the driving shaft 121 contacts one position of the supporting spring 11, and contacts two positions of the slider 13. When no current is supplied to the piezoelectric element 122, the lens holder 5 is stationary with respect to the driving shaft 121. The other end of the support spring 11 is positioned on the opposite side of the drive shaft 121 on the lens holder 5. The support spring 11 may be any type of elastomer and the slider 13 may be any type of support structure. The material, shape and mounting location of the elastomer and the support structure are not limited as long as the elastomer pushes the drive shaft 121 to the support structure.

The AF drive engine unit 12 (fig. 2) is an impact drive mechanism using the piezoelectric element 122. The operating principle is as follows: the piezoelectric element 122 contracts or expands according to the direction of the voltage to be applied, and the magnitude and speed of the contraction or expansion depend on the waveform. When the piezoelectric element 122 is driven in a predetermined direction by a waveform having a slowly rising curve, the piezoelectric element 122 is slowly expanded, and the driving shaft 121 is slowly moved upward together with the lens holder 5. When the piezoelectric element 122 is driven in the other direction by a waveform having a fast rising curve (a fast falling curve in consideration of the above-mentioned predetermined direction), the piezoelectric element 122 contracts rapidly, the driving shaft 121 moves down rapidly, and the lens holder 5 does not move. In this expansion and contraction operation, the lens holder 5 is lifted up and held stationary by inertia. By repeating this operation, the lens holder 5 is gradually moved upward.

If the above-described expansion and contraction operations are performed in the opposite directions, i.e., the piezoelectric element 122 is driven by a waveform having a slowly falling curve and a waveform having a rapidly rising curve (in view of the above-described predetermined direction), the lens holder 5 is lowered and kept stationary due to inertia. By repeating this reverse operation, the lens holder 5 is gradually moved downward. In summary, the lens holder 5 can be moved upward and downward as needed.

As can be seen from fig. 2, since the magnetic force of the magnet 7 pulls the magnetic core 10 (hereinafter, also referred to as "core yoke") fixed to the moving base 2 through the Flexible Printed Circuit (FPC) 9, unnecessary rotation of the lens holder 5 about the driving shaft 121 can be suppressed. The magnetic flux passes through the magnetic core 10 and prevents magnetic leakage. The magnetic core 10 is made of iron or a material having a high magnetic permeability, such as permalloy.

As shown in FIG. 1, the OIS system is implemented using SMA in the "d" direction and VCM in the "r" direction.

Two SMA wires 1-R and 1-L are used as OIS for the "d" direction. One end of the SMA wire 1-R is fixed to a fixing point 17a on the fixing base 4, and the other end is fixed to a fixing point 17b on the fixing base 4. The middle of the SMA wire 1-R is hooked around the point of action 17 on the moving base 2. Similarly, the SMA wires 1-L are fixed at one end to a fixing point 16a on the fixing base 4 and at the other end to a fixing point 16b on the fixing base 4. The middle of the SMA wires 1 to L is hooked around the point of action 16 on the moving base 2. In another embodiment, the

fixed points

16a, 16b, 17a and 17b may be provided on the moving base 2 and the action points 16 and 17 may be provided on the fixed base 4.

When current is applied to the SMA wires 1-L, the SMA wires 1-L contract. On the other hand, since no current is applied to the SMA wire 1 to R, the wire can be lengthened. Accordingly, the moving base 2 moves in the right-downward direction in fig. 1 with respect to the fixed base 4. When current is applied to the SMA wires 1-R, the SMA wires 1-R contract. On the other hand, since no current is applied to the SMA wires 1 to L, the wires can be lengthened. Accordingly, the moving base 2 moves in the upper left direction in fig. 1 with respect to the fixed base 4. By alternately applying current to the two lines 1-L and 1-R, the mobile base 2 can be moved in a reciprocating motion in the direction "d". In order to guide the moving base 2 in the "d" direction,

grooves

18, 20, 22 and 24 are provided on the rear side of the moving base 2 and the stationary base 4, and

balls

19, 21, 23 and 25 are provided between the rear side of the moving base 2 and the corresponding grooves on the stationary base 4. Fig. 3 shows a cross-sectional view of the groove 18(18a and 18b) and the ball 19 along a chain line from the upper right to the lower left in fig. 1. The shapes of the grooves 20(20a and 20b) and the balls 21 are the same as those in fig. 3. Fig. 4 shows a cross-sectional view of the groove 22(22a and 22b) and the ball 23 along a chain line from the upper left to the lower right in fig. 1. The

grooves

22a and 22b are circular in plan view. The diameter of the groove 22a may be determined according to the moving range of the "d" direction. The balls 25 and corresponding grooves 24(24a and 24b) shown in fig. 2 are not shown in fig. 1. The shape of the groove 24(24a and 24b) is the same as that of the groove 22(22a and 22b) shown in fig. 4. The guide rail is not limited to the above-described structure. Various configurations of guide rails may be employed. In another embodiment, no guide rails may be provided.

VCM is used as OIS in the "r" direction shown in FIG. 1. The VCM swings the lens holder 5. The magnet 7 is mounted on the lens holder 5. In fig. 2, the magnet 7 faces the coil 8 provided on the FPC 9. As the lens holder 5 moves up and down, the magnet 7 also moves up and down. The coil 8 is dimensioned with a certain margin in view of the movement of the magnet 7. The terminals of the coil 8 are electrically connected to the FPC 9. A combination type coil 8 (referred to as a Flexible Pattern (FP) coil) having an FPC 9 may be used. The magnetic core 10 is disposed on the rear side of the FPC 9. The magnetic core 10 is made of iron or a material having a high magnetic permeability. In another embodiment, the positions of the magnet 7 and the coil 8 may be reversed.

Referring to fig. 1, in order to avoid unnecessary swinging of the lens holder 5, a stopper 14 and a stopper holder 15 are provided. The stopper 14 is fixed to the lens holder 5, and the stopper holder 15 is fixed to the moving base 2. The stopper 14 moves around the drive shaft 121. The inner diameter of the stopper bracket 15 may be determined according to the moving range of the "r" direction. The stopper bracket 15 does not contact the side surface of the stopper 14 except for the case where an impact or the like is applied from the outside. The shape of the stopper 14 is not limited to a circle, and the shape of the stopper bracket 15 is not limited to a part of a circle.

Fig. 5 shows the magnetic core 10 and the coil 8 as viewed from the point (B) shown in fig. 1. In fig. 5, the FPC 9 is not shown. A hall element 30 (not shown in fig. 1 and 2) is provided on the magnetic core 10 to sense the direction and intensity of the magnetic field, thereby detecting the position of the magnet 7. When the lens holder 5 swings around the driving shaft 121, the magnetic core 10 generates a magnetic spring effect, pulling the magnet 7 on the lens holder 5 to the center of the magnetic core 10. Therefore, when the lens holder 5 is not swung, the lens holder 5 is held stationary at a position where the neutral axis of the magnet 7 faces the center of the core 10. In other words, if the magnet 7 leaves this position, the magnet 7 will return to this position due to the magnetic spring effect. The neutral axis is located between the S pole and the N pole, and the magnetic flux density becomes zero at the neutral axis. Fig. 6 shows the magnet 7 at the rear of the core 10 and the coil 8 as viewed from the point (B) shown in fig. 1. As can be seen from fig. 1, the N and S poles of the other magnet are connected behind the S and N poles shown in fig. 6. The magnetic flux comes from the N pole behind the S pole shown on the left side of the magnet 7 in fig. 6 and enters the S pole shown on the left side of the magnet 7 in fig. 6. That is, the direction of the magnetic field is from front to back in the left front of the magnet 7 in fig. 6. The other flux comes from the N pole shown on the right side of the magnet 7 in fig. 6 and enters the S pole behind the N pole shown on the right side of the magnet 7 in fig. 6. That is, the direction of the magnetic field is from the rear to the front at the right side of the magnet 7 in fig. 6. In this structure, the magnetic flux circuit becomes short and the magnetic leakage is reduced.

When current is applied to the coil 8 in a Clockwise (CW) direction (fig. 5), at the location of the left hand part of the coil 8, the current flows upwards and the direction of the magnetic field is from front to back (as described above). The electromagnetic interaction according to fleming's left hand rule produces a force that moves the coil 8 from right to left. At the position of the right part of the coil 8, the current flows downwards and the magnetic field direction is from back to front (as described above). The electromagnetic interaction according to fleming's left hand rule produces a force that moves the coil 8 from right to left. Since the coil 8 is fixed, the magnet 7 moves in the right direction in fig. 6, i.e., the lens holder 5 swings upward in the right direction in fig. 1.

When a current is applied to the coil 8 in a counter-clockwise (CCW) direction (fig. 5), at the position of the left-hand part of the coil 8, the current flows downwards and the direction of the magnetic field is from front to back (as described above). The electromagnetic interaction according to fleming's left hand rule generates a force that moves the coil 8 from left to right. At the position of the right part of the coil 8, the current flows upwards and the magnetic field direction is from back to front (as described above). The electromagnetic interaction according to fleming's left hand rule generates a force that moves the coil 8 from left to right. Since the coil 8 is fixed, the magnet 7 moves in the left direction in fig. 6, that is, the lens holder 5 swings in the left-downward direction in fig. 1. In summary, the lens holder 5 can swing in two directions.

Using this OIS system implemented with SMA in the "d" direction and VCM in the "r" direction around the drive shaft 121, the center position of the lens can be moved in two dimensions at any position on the polar coordinate system.

The frictional resistance of the AF drive engine unit 12 can be reduced by using the dither technique. Fig. 7 shows the thrust movement of the AF drive engine unit 12. In order to achieve a low and stable μ value (the μ value is defined in the dither technique) between the drive shaft 121 and other objects (the support spring 11 and the slider 13) and to avoid the stick-slip phenomenon, a voltage having a sinusoidal waveform exceeding 200Hz (preferably, 200 to 300Hz) is applied to the coil 8 of the VCM in addition to the 10 to 15Hz voltage of the above-described OIS in the "r" direction, and the like. In fig. 7, a 200Hz wobbling movement is applied to the lens holder 5, i.e. the lens holder 5 is wobbling at a frequency of 200 Hz. Fig. 8 shows a relationship between the speed of the drive shaft 121 and the incident amount (the moving distance of the lens holder 5 with respect to the drive shaft 121) at the time of no/shake.

When the driving shaft 121 moves rapidly and the lens holder 5 remains stationary, assume that the weight 123 has a weight M₁And the weight of the driving shaft 121 is M₂Velocity V of weight 123₁And the speed V of the drive shaft 121₂Substantially satisfies M₁V₁+M₂V₂0, i.e. theoretically M₁V₁＝–M₂V₂. When the drive shaft 121 moves rapidly, the frictional resistance becomes low but remains at a certain level, and therefore the amount of incidence is limited, as shown in the left diagram in fig. 8. By the influence of the shake, the frictional resistance is reduced, the average speed of the thrust motion to achieve a larger incident amount is increased, and the dispersion of the speed is reduced. That is, the AF control can be increased and stabilized, and the current consumption of AF can be reduced.

The reality of a dual-camera system is that the dual cameras are focused on the same object. When the hand shake occurs, the lens holder 5 is moved to an appropriate position calculated correctly for the right-side camera based on the gyro signal of the right-side camera and the AF position information. The OIS distance for the left camera may be different from the OIS distance for the right camera because the optical factors may be different and the AF position (infinity to macro) may be different. In this case of the dual OIS system, the OIS system moves to the appropriate location, respectively. Two different OIS systems are required. A conventional OIS system is a moving magnet system in which a magnet moves. When two conventional OIS systems are placed side by side, the two systems exert a magnetic influence on each other because of the magnetic field leakage that occurs in the moving magnet type OIS system. Therefore, OIS actuators without the influence of magnetic fields are needed. OIS actuators are needed that have no magnetic field effect and achieve high compensation ratios (e.g., over 30 dB). The compensation ratio indicates the degree of correction of hand shake. With a compensation ratio of 30dB, the image appears to be motionless. To reduce or eliminate the magnetic field effects, an SMA system is applied only to the "d" direction, and a very small VCM system is applied only to the "r" direction. This magnetic field is small and has little effect because the magnet has a small size, is magnetized into two poles, and faces the core yoke (e.g., iron or permalloy). Although the SMA system may take up space, the SMA wires may produce sufficient anti-friction. Therefore, OIS performance (especially the compensation ratio) is good even with SMA systems. Furthermore, the current consumed by the present invention is much less than conventional VCM AF and OIS.

By means of the invention, OIS actuators can be realized which reduce or eliminate the influence of magnetic fields and which achieve a high compensation ratio (e.g. over 30 dB). To reduce or eliminate the magnetic field effects, SMA and rolling-type miniature VCM are used as OIS systems. Meanwhile, by applying the impact piezo type, the total current consumption is much less than the conventional VCM AF and OIS, as shown in the following table:

TABLE 1

Circuit estimation	During movement	Stopping at a 1m focal point	Lens position control
				Conventional VCM AF	40mA	15mA
BumpingPiezoelectric device	3.5mA	0mA
				Conventional OIS	80mA		50mA
SMA+VCM	15mA		25mA

When two lens actuators are used, they may be arranged in different directions. Fig. 9 and 10 show example arrangements of two lens actuators provided by the present invention. Although the two lens actuators in fig. 9 are arranged in the same direction, in fig. 10, the left lens actuator is located in the opposite direction, i.e., the left lens actuator is rotated 180 degrees from the position in fig. 9. The left lens actuator may be rotated 90 degrees clockwise or counterclockwise from the position in fig. 9, or the right lens actuator may be rotated 90 degrees counterclockwise from the position in fig. 9. In these structures, the distance between the magnet 7 of the left lens actuator and the magnet 7 of the right lens actuator is longer than that in fig. 9.

The foregoing disclosure is only illustrative of the present invention and is, of course, not intended to limit the scope of the invention. It will be understood by those of ordinary skill in the art that all or a portion of the flow chart for implementing the above embodiments and equivalent modifications made according to the claims of the present invention shall fall within the scope of the present invention.

Claims

1. A lens actuator, comprising:

a piezoelectric element for moving the lens holder in the optical axis direction;

a Shape Memory Alloy (SMA) for moving the lens holder in a predetermined direction perpendicular to the optical axis direction; and

a Voice Coil Motor (VCM) for moving the lens holder in a direction perpendicular to the optical axis direction and different from the predetermined direction; a magnet of the VCM is fixed on the lens holder, and a coil of the VCM is fixed on a moving base to face the magnet;

and a magnetic core located at the rear side of the coil and having a high magnetic permeability, the magnet and the magnetic core being configured to suppress rotation of the lens holder.

2. A lens actuator as claimed in claim 1, wherein one end of the piezoelectric element is coupled to the driving shaft, the lens holder includes an elastic body and a support structure, and the elastic body pushes the driving shaft toward the support structure.

3. A lens actuator according to claim 2, wherein a waveform for reducing friction between the driving shaft and the support structure and the elastic body is superimposed on a waveform applied to the VCM for correcting hand shake.

4. A lens actuator as claimed in claim 2 or 3, wherein the other end of the piezoelectric element is coupled to a weight coupled to the movable base, and

the SMA contracts according to the voltage to be applied and moves the moving base relative to the fixed base.

5. A lens actuator as claimed in claim 4, further comprising a guide rail between the moving base and the fixed base.

6. A lens actuator as claimed in any one of claims 1 to 3, wherein the neutral axis of the magnet is directed towards the centre of the core.

7. An electronic device comprising two lens actuators according to any one of claims 1 to 6 arranged side by side in one plane.

8. The electronic device of claim 7, wherein the two lens actuators are placed in different directions such that the distance between the magnets is greater than when the magnets are placed in the same direction.