WO2018223382A1

WO2018223382A1 - Lens actuator with ois and af function

Info

Publication number: WO2018223382A1
Application number: PCT/CN2017/087755
Authority: WO
Inventors: Masaru Uno; Atsushi Yoneyama
Original assignee: Huawei Technologies Co., Ltd.
Priority date: 2017-06-09
Filing date: 2017-06-09
Publication date: 2018-12-13
Also published as: CN110692234B; CN110692234A

Abstract

A lens actuator includes: a piezoelectric element (122) for moving a lens holder (5) in an optical axis direction, a Shape Memory Alloy (SMA) (1-R, 1-L) for moving the lens holder (5) in a predetermined direction (d) that is perpendicular to the optical axis direction, and a Voice Coil Motor (VCM) (7,8) for moving the lens holder (5) in a direction (r) that is perpendicular to the optical axis direction and different from the predetermined direction (d). An imaging device reduces or eliminates magnetic influence by an OIS system.

Description

LENS ACTUATOR WITH OIS AND AF FUNCTION

TECHNICAL FIELD

The present invention relates to a lens actuator with an Optical Image Stabilizer (OIS) and an Auto Focus (AF) function, used for an imaging device.

BACKGROUND

In a camera, the AF function is used for focusing an image to be shot on an image sensor by moving a lens in an optical axis direction (the direction in which the centers of lenses are put in a line) , and the OIS is used for suppressing the image from being blurred, which is caused by hand shaking when taking a photo, by moving the lens in the direction perpendicular to the optical axis.

An OIS system of a camera module is becoming popular in the smart phone market, because everyone can take a beautiful picture even in a dark place or in case of hand shaking by using the OIS system. On the other hand, a Dual camera system is also becoming popular in the smart phone market, because by using the Dual camera system, various applications such as Zoom, 3D, and AF control can be realized. Since there is a strong possibility that these two trends will merge, the Dual OIS system will be needed in the near future. A conventional OIS system has a problem of magnetic field leakage because of a moving magnet system. A breakthrough invention against this leakage problem is needed. At the same time, downsizing technology is needed, and also reducing current consumption is strongly needed.

The conventional OIS system has a problem of magnetic field leakage. In case of a Dual camera, an actuator next to an OIS actuator must be modified to a yoke type AF actuator. In this type, the yokes and AF magnet are located as far as possible from the OIS system. In case of the Dual OIS system, two OIS systems cannot be located side by side, because the OIS systems have a bad influence on each other due to magnetic field leakage.

SUMMARY

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

The present invention is a system that has a piezoelectric element system for AF, and a moving system for a diagonal direction by using SMA wires and a moving system for the direction perpendicular to the diagonal direction by using a VCM for OIS. The present invention relates to VCM, SMA, and Piezoelectric technologies. In particular, the actuator module comprises two OIS actuators and one AF actuator on one base. The present invention includes a piezoelectric element AF actuator and a CSV (Combined SMA and VCM) OIS actuator. Therefore, one purpose of this invention is to provide a Dual OIS system without the problem of magnetic field leakage. The other purpose of this invention is to reduce the current consumption of the whole actuator system in use. As a Dual camera module system, the important purpose of this invention is to provide a high quality picture that is merged from two different sensors.

According to a first aspect, a lens actuator is provided, where the lens actuator includes: a piezoelectric element for moving a lens holder in an optical axis direction, a Shape Memory Alloy (SMA) for moving the lens holder in a predetermined direction that is perpendicular to the optical axis direction, and a Voice Coil Motor (VCM) for moving the lens holder in a direction that is perpendicular to the optical axis direction and different from the predetermined direction. In this constitution, the influence of the magnetic field can be reduced.

In a first possible implementation manner of the first aspect, one end of the piezoelectric element is coupled to a drive shaft, the lens holder comprises an elastic body and a supporting structure, and the elastic body pushes the drive shaft to the supporting structure. This constitution allows the lens holder to move in an optical axis direction and also swing around the drive shift.

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 drive shaft, and the supporting structure and the elastic body is superposed on a waveform applied to the VCM for correcting for hand shaking. In this constitution, 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, another end of the piezoelectric element is coupled to a weight, the weight is coupled to a moving base, and the SMA contracts depending on the voltage to be applied and moves the moving base in relation to a fixing base. In this constitution, the moving base can be moved without a 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 between the moving base and the fixing base. In this constitution, the direction of the movement can be stabilized.

With reference to the first aspect or the first to fourth possible implementation manner of the first aspect, in a fifth possible implementation manner of the first aspect, a magnet of the VCM is fixed to the lens holder, a coil of the VCM is fixed to the moving base so as to face the magnet, and the lens actuators include a core having high magnetic permeability on the back side of the coil. The magnetic field leakage can be suppressed by using a core having high magnetic permeability.

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 core. In this constitution, the neutral axis of the magnet is pulled to the position facing the center of the core.

With reference to the first aspect or the first to sixth possible implementation manner of the first aspect, in a seventh possible implementation manner of the first aspect, an electronic device including two lens actuators side by side in a plane is provided. In this constitution, various dual camera systems can be implemented with the reduced magnetic field leakage.

With reference to the seventh possible implementation manner of the first aspect, in a eighth possible implementation manner of the first aspect, the two lens actuators are placed in different directions so that the distance between the magnets is longer than that of the case where they are placed in the same direction. In this constitution, since the distance between the magnets becomes longer, the influence of the magnetic field can be reduced.

BRIEF DESCRIPTION OF DRAWINGS

To describe the technical solutions in the embodiments of the present invention or in the prior art more clearly, the following briefly introduces the accompanying drawings required for describing the embodiments or the prior art. Apparently, the accompanying drawings in the following description show merely some embodiments of the present invention, and a person of ordinary skill in the art may still derive other drawings from these accompanying drawings without creative efforts.

FIG. 1 illustrates a top view of a lens actuator according to the present invention；

FIG. 2 illustrates a side view of the lens actuator viewed from point (A) shown in FIG. 1；

FIG. 3 illustrates a cross sectional view of the groove 18 (18a and 18b) and the ball 19 along the dot-and-dash line from the upper right to the lower left in Fig. 1；

FIG. 4 illustrates a cross sectional view of the groove 22 (22a and 22b) and the ball 23 along the dot-and-dash line from the upper left to the lower right in Fig. 1；

FIG. 5 illustrates the core 10 and the coil 8 viewed from point (B) shown in Fig. 1；

FIG. 6 illustrates the magnet 7 behind the core 10 and the coil 8 viewed from point (B) shown in Fig. 1；

FIG. 7 illustrates thrust motion by the AF drive engine unit 12；

FIG. 8 illustrates the relationship between the velocity and the incidence without/with dithering；

FIG. 9 illustrates an example arrangement of two lens actuators； and

FIG. 10 illustrates another example arrangement of two lens actuators.

DESCRIPTION OF EMBODIMENTS

The following clearly and completely describes the technical solutions in the embodiments of the present invention with reference to the accompanying drawings in the embodiments of the present invention. The described embodiments are merely some but not all of the embodiments of the present invention. All other embodiments obtained by a person of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the scope of protection of the present invention.

The features of the present invention are novel. The drawings are for illustration purposes only and are not drawn to scale. Furthermore, like numbers represent like features in the drawings. The present invention itself, both as to structure 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 according to the present invention, and Fig. 2 shows a side view of the lens actuator viewed from point (A) shown in Fig. 1. In Fig. 2, a fixing base 4 is fixed to, for example, a camera module of a smartphone. An object to be shot is taken to be in the top portion in Fig. 2, and an image sensor is provided below the fixing base 4. The center of the moving base 2 and the center of the fixing base 4 are opened enough to allow light from the lenses to pass through to the image sensor.

In Fig. 2, an AF drive engine unit 12 includes a drive shaft 121, a piezoelectric element 122, and a weight 123. Wires for supplying 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. This AF drive engine unit 12 moves a lens holder 5 upward or downward. The lens holder 5 has a lens barrel 6 inside, and the lens barrel 6 has several lenses inside.

Referring to Fig. 1, one end of a backup spring 11 pushes the drive shaft 121 to the V shape area of sliders 13 (13a and 13b) , and the drive shaft 121 is grasped by the backup spring 11 and the sliders 13. Namely, the drive shaft 121 contacts the backup spring 11 at one place and the sliders 13 at two places. When current is not supplied to the piezoelectric element 122, the lens holder 5 is static in relation to the drive shaft 121. Another end of the backup spring 11 is positioned at the opposite side of the drive shaft 121 on the lens holder 5. The backup spring 11 may be any kind of elastic body, and the sliders 13 may be any kind of supporting structure. The materials, shapes, and mounting positions of the elastic body and the supporting structure are not limited, as long as the elastic body pushes the drive shaft 121 to the supporting 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 depending on the direction of the voltage to be applied, and the magnitude and the speed of contracting or expanding depend on the waveform. When the piezoelectric element 122 is driven by a waveform having a slow rising curve in a predetermined direction, the piezoelectric element 122 expands slowly, and the drive shaft 121 moves upward slowly together with the lens holder 5. When the piezoelectric element 122 is driven by a waveform having a rapid rising curve in another direction (rapid falling curve in view of the above-mentioned predetermined direction) , the piezoelectric element 122 contracts quickly, and the drive shaft 121 moves downward quickly not with the lens holder 5. In this expanding and contracting operation, the lens holder 5 is lifted up and left behind due to inertia. By repeating this operation, the lens holder 5 gradually moves upward.

If the above-mentioned expanding and contracting operation is performed in the opposite direction, namely, the piezoelectric element 122 is driven by a waveform having a slow falling curve and a waveform having a rapid rising curve in view of the above-mentioned predetermined direction, the lens holder 5 is lowered down and left behind due to inertia. By repeating this opposite operation, the lens holder 5 gradually moves downward. From the above, the lens holder 5 can be moved upward and downward as desired.

As can be seen from Fig. 2, since the magnetic force of a magnet 7 pulls a core 10 (hereinafter, also referred to as “core yoke” ) fixed on the moving base 2 by means of a flexible printed circuit (FPC) 9, unnecessary rotation of the lens holder 5 around the drive shaft 121 can be suppressed. Magnetic flux passes through the core 10 and magnetic leakage is prevented. The core 10 is made of iron or a material having high magnetic permeability, for example, Permalloy.

As shown in Fig. 1, an OIS system is implemented by using SMAs for the “d” direction and a VCM for the “r” direction.

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

points

16a, 16b, 17a, and 17b may be provided on the moving base 2, and the points of

application

16 and 17 may be provided on the fixing base 4.

When current is applied to the SMA wire 1-L, it contracts. On the other hand, since current is not applied to the SMA wire 1-R, it can be extended. Accordingly, the moving base 2 moves in the lower right direction in Fig. 1 in relation to the fixing base 4. When current is applied to the SMA wire 1-R, it contracts. On the other hand, since current is not applied to the SMA wire 1-L, it can be extended. Accordingly, the moving base 2 moves in the upper left direction in Fig. 1 in relation to the fixing base 4. By applying current to these two wires 1-L and 1-R alternately, the moving base 2 can move in the “d” direction in a round trip motion.

In order to guide the moving base 2 in the “d” direction,

grooves

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

balls

19, 21, 23, and 25 are put between corresponding grooves on the back side of the moving base 2 and on the fixing base 4. Fig. 3 shows a cross sectional view of the groove 18 (18a and 18b) and the ball 19 along the dot-and-dash line from the upper right to the lower left in Fig. 1. The shapes of the groove 20 (20a and 20b) and the ball 21 are identical to those in Fig. 3. Fig. 4 shows a cross sectional view of the groove 22 (22a and 22b) and the ball 23 along the dot-and-dash line from the upper left to the lower right in Fig. 1. The

grooves

22a and 22b have a round shape in the top view. The diameter of the groove 22a may be determined based on the range of the movement of the “d” direction. A ball 25 shown in Fig. 2 and corresponding groove 24 (24a and 24b) are not shown in Fig. 1. The shape of the groove 24 (24a and 24b) are identical to the groove 22 (22a and 22b) shown in Fig. 4. The guide is not limited to the above-mentioned structure. Various structures of the guide may be adopted. In another embodiment, the guide may not be provided.

One VCM is used as an OIS for 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 a coil 8 provided on the FPC 9. Since the lens holder 5 moves upward and downward, the magnet 7 also moves upward and downward. The size of the coil 8 is determined to have a margin in consideration of the movement of the magnet 7. The terminals of the coil 8 are electrically connected to the FPC 9. A combined type coil 8 with FPC 9 (called a flexible patterning (FP) coil) may be used. The core 10 is provided on the back side of the FPC 9. The core 10 is made of iron or a material having high magnetic permeability. In another embodiment, the positions of the magnet 7 and the coil 8 may be exchanged.

Referring to Fig. 1, in order for the lens holder 5 not to swing more than necessary, a stopper 14 and a stopper holder 15 are provided. The stopper 14 is fixed on the lens holder 5, and the stopper holder 15 is fixed on the moving base 2. The stopper 14 moves around the drive shaft 121. The inside diameter of the stopper holder 15 may be determined based on the range of the movement of the “r” direction. The stopper holder 15 does not contact the side of the stopper 14 except in the case where, for example, a shock is given from outside. The shape of the stopper 14 is not limited to a circle and the shape of the stopper holder 15 is not limited to a part of a circle.

Fig. 5 shows the core 10 and the coil 8 viewed from point (B) shown in Fig. 1. In Fig. 5, the FPC 9 is not shown. A hall element 30 is provided on the core 10 (not shown in Figs. 1 and 2) to sense the direction and the strength of the magnetic field in order to detect the position of the magnet 7. The core 10 yields the magnetic spring effect of pulling the magnet 7 on the lens holder 5 to the center of the core 10 when the lens holder 5 swings around the drive shaft 121. Accordingly, when the lens holder 5 does not swing, the lens holder 5 remains stationary at the position where the neutral axis of the magnet 7 faces the center of the core 10. In other words, if the magnet 7 gets out of this position, it is put back to this position due to the magnetic spring effect. The neutral axis is between the S pole and N pole, and the magnetic flux density becomes zero at the neutral axis. Fig. 6 shows the magnet 7 behind the core 10 and the coil 8 viewed from point (B) shown in Fig. 1. As can be seen from Fig. 1, the N pole and S pole of another magnet are attached behind the S pole and N pole shown in Fig. 6. Magnetic flux comes out of the N pole behind the S pole shown in the left side of the magnet 7 in Fig. 6, and goes into the S pole shown in the left side of the magnet 7 in Fig. 6. Namely, in front of the left side of the magnet 7 in Fig. 6, the direction of the magnetic field is from the front to the back. The other magnetic flux comes out of the N pole shown in the right side of the magnet 7 in Fig. 6, and goes into the S pole behind the N pole shown in the right side of the magnet 7 in Fig. 6. Namely, in front of the right side of the magnet 7 in Fig. 6, the direction of the magnetic field is from the back to the front. In this constitution, the loop of magnetic flux becomes short, and magnetic leakage is reduced.

When current is applied to the coil 8 in the clockwise (CW) direction (Fig. 5) , at the position of the left part of the coil 8, the current flows upward, and the direction of the magnetic field is from the front to the back as mentioned above. According to the electromagnetic interaction of Fleming’s left hand rule, the force to move the coil 8 from right to left yields. At the position of the right part of the coil 8, the current flows downward, and the direction of the magnetic field is from the back to the front as mentioned above. According to the electromagnetic interaction of Fleming’s left hand rule, the force to move the coil 8 from right to left yields. Since the coil 8 is fixed, the magnet 7 moves in the right direction in Fig. 6, namely, the lens holder 5 swings in the upper right direction in Fig. 1.

When current is applied to the coil 8 in the counter-clockwise (CCW) direction (Fig. 5) , at the position of the left part of the coil 8, the current flows downward, and the direction of the magnetic field is from the front to the back as mentioned above. According to the electromagnetic interaction of Fleming’s left hand rule, the force to move the coil 8 from left to right yields. At the position of the right part of the coil 8, the current flows upward, and the direction of the magnetic field is from the back to the front as mentioned above. According to the electromagnetic interaction of Fleming’s left hand rule, the force to move the coil 8 from left to right yields. Since the coil 8 is fixed, the magnet 7 moves in the left direction in Fig. 6, namely, the lens holder 5 swings in the lower left direction in Fig. 1. From the above, the lens holder 5 can be swung in both directions.

Using this OIS system implemented by the SMAs for the “d” direction and the VCM for the “r” direction around the drive shaft 121, the center position of the lens can be moved anywhere in two dimensions on the polar coordinate system.

In order to reduce the frictional resistance of the AF drive engine unit 12, Dithering technology can be utilized. Fig. 7 shows thrust motion by the AF drive engine unit 12. To achieve a low and stable μ value (μ value is defined in Dithering technology) between the drive shaft 121 and other things (the backup spring 11 and the sliders 13) and to avoid stick slip phenomena, a voltage having a sine waveform over 200 Hz, preferably, 200 to 300 Hz, is applied to the coil 8 of the VCM in addition to the voltage of, for example, 10 to 15 Hz for the above-mentioned OIS for the “r” direction. In Fig. 7, a 200-Hz dithering swing motion is applied to the lens holder 5, namely, the lens holder 5 is swung at 200 Hz. Fig. 8 shows the relationship between the velocity of the drive shaft 121 and the incidence (moving distance of the lens holder 5 in relation to the drive shaft 121) without/with dithering.

When the drive shaft 121 quickly moves and the lens holder 5 is left behind, assuming that the weight of the weight 123 is M₁ and the weight of the drive shaft 121 is M₂, velocity V₁ of the weight 123 and velocity V₂ of the drive shaft 121 substantially satisfy M₁V₁+M₂V₂＝0, namely, M₁V₁＝-M₂V₂ in theory. When the drive shaft 121 quickly moves, frictional resistance becomes low, but remains to a certain extent, and thus the incidence is limited as shown in the left graph in Fig. 8. By the effect of Dithering, frictional resistance is lowered, the average velocity of the thrust motion to achieve long incidence increases, and the dispersion of velocity decreases. Namely, AF control can be improved and stabilized, and current consumption for AF can be reduce.

As an actual situation of a Dual camera system, dual cameras focus on the same subject. When hand shaking happens, according to a Gyro signal and AF position information of the right side camera, the lens holder 5 moves to the suitable position that is calculated correctly for the right side camera. The OIS distance for the left side camera may be different from that of the right side camera because an optical factor may be different and AF position (infinity to macro) may be different. In such a situation for the Dual OIS system, the OIS systems move to the suitable position separately. Two different OIS systems are needed. The conventional OIS system is a Moving Magnet type, in which magnets move. When two conventional OIS systems are placed side by side, two systems exert a magnetic influence on each other because magnetic field leakage occurs in the Moving Magnet type OIS. Accordingly, an OIS actuator without magnetic field influence is needed. An OIS actuator without magnetic field influence that achieves a high compensation ratio, for example, over 30 dB is needed. The compensation ratio indicates the degree of correction of hand shaking, and images appear not to be moving at a compensation ratio of 30 dB. To reduce or eliminate magnetic field influence, an SMA system is applied for only the “d” direction, and a very small VCM system is applied for only the ‘r’ direction. This magnetic field is very small and has little magnetic field influence because the magnet size is very small and is magnetized as two poles, and faces the core yoke (for example, iron or Permalloy) . Although this SMA system can take up space, SMA wires can generate enough power against friction. Therefore, even in case of an SMA system, OIS performance (especially, compensation ratio) should be good. Moreover, from viewpoint of current consumption, the present invention is much better than conventional VCM AF and OIS.

The OIS actuator with reduced or eliminated magnetic field influence that achieves a high compensation ratio (for example over 30 dB) can be achieved by using the present invention. To reduce or eliminate magnetic field influence, as an OIS system, an SMA and a rolling type small VCM are applied. At the same time, by applying the Impact piezoelectric type, total current consumption is much better than conventional VCM AF and OIS as shown in the following table:

Current estimation	During moving	Stop at 1 m focus	Lens position control
Conventional VCM AF	40 mA	15 mA
Impact piezoelectric	3.5 mA	0 mA
Conventional OIS	80 mA		50 mA
SMA+VCM	15 mA		25 mA

Table 1

When using two lens actuators, they may be arranged in different directions. Fig. 9 and Fig. 10 show example arrangements of two lens actuators according to the present invention. Although the two lens actuators in Fig. 9 are arranged in the same direction, in Fig. 10, the left one is in the opposite direction, namely, the left one is rotated by 180 degrees from the position in Fig. 9. The left one may be rotated by 90 degrees clockwise or counter-clockwise from the position in Fig. 9, or the right one may be rotated by 90 degrees counter-clockwise from the position in Fig. 9. In these constitutions, the distance between the magnet 7 of the left one and the magnet 7 of the right one is longer than that in Fig. 9.

Disclosed above are merely exemplary embodiments of the present invention, and certainly are not intended to limit the scope of protection of the present invention. A person of ordinary skill in the art may understand that all or some of the processes that implement the foregoing embodiments and equivalent modifications made in accordance with the claims of the present invention shall fall within the scope of the present invention.

Claims

A lens actuator, comprising:

a piezoelectric element for moving a lens holder in an optical axis direction,

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

a Voice Coil Motor (VCM) for moving the lens holder in a direction that is perpendicular to the optical axis direction and different from the predetermined direction.
The lens actuator according to claim 1, wherein one end of the piezoelectric element is coupled to a drive shaft, the lens holder comprises an elastic body and a supporting structure, and the elastic body pushes the drive shaft to the supporting structure.
The lens actuator according to claim 2, wherein a waveform for reducing friction between the drive shaft, and the supporting structure and the elastic body is superposed on a waveform applied to the VCM for correcting for hand shaking.
The lens actuator according to claim 2 or 3, wherein another end of the piezoelectric element is coupled to a weight, the weight being coupled to a moving base, and

the SMA contracts depending on a voltage to be applied, and moves the moving base in relation to a fixing base.
The lens actuator according to claim 4, further comprising a guide between the moving base and the fixing base.
The lens actuator according to any one of claims 1 to 5, wherein a magnet of the VCM is fixed to the lens holder, a coil of the VCM is fixed to the moving base so as to face the magnet, and the lens actuator comprises a core having high magnetic permeability on the back side of the coil.
The lens actuator according to claim 6, wherein the neutral axis of the magnet faces the center of the core.
An electronic device comprising two lens actuators according to any one of claims 1 to 7 side by side in a plane.
The electronic device according to claim 8, wherein the two lens actuators are placed in different directions so that the distance between the magnets is longer than that of the case where they are placed in the same direction.