Abstract:
In a camera where the lens or image sensor is laterally moved in a carrier to shift the image for compensating for unwanted camera movement, a reflection surface is used to reflect light, and a photo-emitter/sensor pair is used to illuminate the reflection surface and to detect reflected light therefrom. Reflection surface is provided near the edge of one carrier section e and photo-emitter/sensor pair is disposed on another carrier section. These sections are movable relative to each other for imaging shifting purposes. The photo-emitter/sensor pair is positioned such that the light cone emitted by the photo-emitter partly hits the V reflection surface and partly falls beyond the edge. As the photo-emitter/sensor pair and the reflection surface move relative to each other, the area on the reflection surface illuminated by the photo-emitter changes causing a change in the amount of detected light.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates generally to optical position sensing in an imaging system and, more particularly, to position sensing for the optical image stabilizer. 
       BACKGROUND OF THE INVENTION 
       [0002]    Imaging applications such as optical image stabilizers, optical zoom systems and auto-focus lens systems require high precision in position sensing. In general, needed accuracy is in the order of few microns. Sensor output linearity and immunity to external disturbances is important. Furthermore, the operation mode for position sensing also requires non-contact operation to avoid mechanical wear. 
         [0003]    Optical image stabilization generally involves laterally shifting the image projected on the image sensor in compensation for the camera motion. Shifting of the image can be achieved by one of the following general techniques: 
         [0004]    Lens shift—this optical image stabilization method involves moving one or more lens elements of the optical system in a direction substantially perpendicular to the optical axis of the system; 
         [0005]    Image sensor shift—this optical image stabilization method involves moving the image sensor in a direction substantially perpendicular to the optical axis of the optical system; 
         [0006]    Camera module tilt—this method keeps all the components in the optical system unchanged while tilting the entire module so as to shift the optical axis in relation to a scene. 
         [0007]    In any one of the above-mentioned image stabilization techniques, a mechanism is required to effect the change in the optical axis or the shift of the image sensor by moving at least one of the imaging components. Furthermore, a device is used to determine the position of the moved imaging component. 
         [0008]    In prior art, Hall sensors are used where voice coil actuators are used for image stabilization. Alternatively, a reflector with a high reflection area and a low reflection area or a reflector with gray-scale pattern is used for position sensing purposes. 
         [0009]    The present invention provides a different method and device for position sensing. 
       SUMMARY OF THE INVENTION 
       [0010]    The present invention uses a reflection surface to reflect light, and a photo-emitter and photo-sensor pair to illuminate the reflection surface and to detect the reflected light from the reflection surface. In particular, the reflection surface is provided near the edge of a first frame and the photo-emitter/sensor pair is disposed on a second frame. The first and second frames are moved relative to each other when the first frame is used to move one of the imaging components in an imaging system. The photo-emitter/sensor pair is positioned at a distance from the reflection surface such that the light cone emitted by the photo-emitter only partly hits the reflection surface. Part of the light cone misses the reflection surface because it falls beyond the edge. As the photo-emitter/sensor pair and the reflection surface move relative to each other, the area on the reflection surface illuminated by the photo-emitter changes. Accordingly, the amount of light sensed by the photo-sensor also changes. The change in the reflected light amount causes a near-linear output signal response in a certain travel range of the reflection surface. Preferably, the reflectivity of the reflection surface within the illuminated area is substantially uniform and the distance between the photo-emitter/sensor pair and the reflection surface is substantially fixed. As such, the output signal response is substantially proportional to a portion of a circular area of a fixed radius and the portion is reduced or increased as a function of a moving distance as the photo-emitter/sensor pair and the reflection surface move relative to each other. 
         [0011]    In one of the embodiments of the present invention, the diameter of the illuminated area is smaller than the width of the reflection surface. 
         [0012]    In another embodiment of the present invention, the diameter of the illuminated area is equal to or greater than the width of the reflection surface. 
         [0013]    In yet another embodiment of the present invention, the reflection surface has a wedge shape. 
         [0014]    In a different embodiment of the present invention, two photo-emitter/sensor pairs disposed at two reflection surfaces for sensing the relative movement in a differential way. 
         [0015]    The present invention will become apparent upon reading the description taken in conjunction with  FIGS. 3   a  to  14 . 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]      FIG. 1  is a schematic representation of an imaging system wherein the image sensor is moved relative to the lens for optical image stabilization purposes. 
           [0017]      FIG. 2  is a top view of a carrier which is used to shift the image sensor in two directions parallel to the image plane. 
           [0018]      FIG. 3   a  and  3   b  show a fixedly disposed photo-emitter/sensor pair positioned in relationship to a movable frame having a reflection surface near the edge of the frame. 
           [0019]      FIG. 4  shows a photo-emitter/sensor pair positioned in relationship to a movable frame having a reflection surface near an edge of a slot. 
           [0020]      FIG. 5  shows a photo-emitter/sensor pair disposed on a movable frame in relationship to a fixed frame having a reflection surface. 
           [0021]      FIG. 6  shows a plot of output signal against the relative position between a photo-emitter/sensor pair and the reflection surface. 
           [0022]      FIG. 7  shows another embodiment of the present invention. 
           [0023]      FIG. 8  shows yet another embodiment of the present invention. 
           [0024]      FIG. 9  shows two photo-emitter pairs positioned in relationship to two separate reflection surfaces near two edges of a frame. 
           [0025]      FIG. 10  illustrates an imaging system wherein a prism is used to fold the optical axis. 
           [0026]      FIG. 11  illustrates how the prism in the imaging system of  FIG. 11  can be rotated for image stabilization purposes. 
           [0027]      FIG. 12  illustrates a gimballed prism for rotation about two axes. 
           [0028]      FIG. 13  shows a photo-emitter pair positioned for sensing the rotation of the prism about one axis. 
           [0029]      FIG. 14  shows another photo-emitter pair positioned for sensing the rotation of the prism about another axis. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0030]    Imaging applications such as optical image stabilizers, optical zoom systems and auto-focus lens systems require high precision in position sensing. In optical image stabilization, one of the imaging components in the imaging system is shifted parallel to the image plane for reducing image blur as a result of an unwanted movement during the exposure. In order to illustrate how position sensing, according to the present invention, is carried out in an imaging system, as shown in  FIG. 1 , it is assumed that the image sensor is mounted on a carrier so that the image sensor can be moved in the X-direction and the Y-direction. An exemplary carrier is shown in  FIG. 2 . 
         [0031]    As shown in  FIG. 2 , the carrier  10  has an outer frame  20 , an inner frame  30  and a plate  40  for mounting an image sensor  50 . The outer frame  20  has a guide pin  221  and a guide pin  222  fixedly mounted on the frame  20 . The inner frame  30  has a bracket  231  movably engaged with the guide pin  221  and a pair of brackets  232  movably engaged with the guide pin  222  such that the inner frame  30  can be caused to move in the X-direction. Similarly, the inner frame  30  has a guide pin  233  and a guide pin  234  fixedly mounted on the frame  30 . The plate  40  has a bracket  243  movably engaged with the guide pin  233  and a pair of brackets  244  movably engaged with the guide pin  234  such that the plate  40  can be caused to move in the Y-direction. As such, the image sensor  50  can be shifted in both the X and Y directions for optical image stabilization purposes. 
         [0032]    It should be noted that a carrier, similar to that of carrier  10 , can be used to move a lens element, instead of the image sensor  50 , in a direction parallel to the image plane for shifting the image projected on the image sensor  50  for optical image stabilization purposes. 
         [0033]    In order to measure the relative movement in the X-direction between the inner frame  30  and the outer frame  20 , a position sensing system  120 , is used. In order to measure the relative movement in the Y-direction between the plate  40  and the inner frame  30 , a position sensing system  130  is used. 
         [0034]    In one embodiment of the present invention shown in  FIGS. 3   a  and  3   b,  the position sensing system  120  comprises a photo-emitter/sensor pair  60  and a reflection surface  70 . The photo-emitter/sensor pair  60  has a photo-emitting element, such as an LED  62 , for illuminating part of the reflection surface  70 . The emitter/sensor pair  60  also has a photo-sensor  64  to sense the amount light reflected by the reflection surface  70 . As shown in  FIGS. 3   a  and  3   b,  the reflection surface  70  is provided near a corner of the movable inner frame  30  whereas the emitter/sensor pair  60  is fixedly mounted on the outer frame  20  facing the reflection surface  70 . The distance and position between the emitter/sensor pair  60  and the reflection surface  70  is chosen such that the light cone  162  emitted by the photo-emitting element  62  only partially hits the reflection surface  70 . Part of the light cone  162  misses the reflection surface  70  as it falls beyond the edge  32  of the frame  30 . 
         [0035]    Preferably, the reflectivity of the reflection surface within the illuminated area is substantially uniform and the distance, d, between the photo-emitter/sensor pair  60  and the reflection surface  70  is also fixed. As such, the output signal response from the photo-sensor  64  is substantially proportional to a portion of a circular area of a fixed radius and the portion is reduced or increased as a function of a moving distance as the photo-emitter/sensor pair and the reflection surface move relative to each other. 
         [0036]    It should be noted that the edge of a frame is not necessarily formed at a corner of the frame, as shown in  FIGS. 3   a  and  3   b.  The edge can be made with a slot on the frame, for example. As shown in  FIG. 4 , the frame  30  has a slot  34  with an edge  36 . The photo-emitter/sensor pair  60  is positioned on the outer frame  20  near the slot  34  so that the light cone emitted by the photo-emitter  62  hits only part of the reflection surface  70 . 
         [0037]    In  FIGS. 3   a  to  4 , the reflection area  70  is depicted as being provided on the inner frame  30  which is movably mounted on the fixed outer frame  20  for linear movement. It should be noted that, the reflection area  70  can also be provided on the fixed outer frame  20  while the photo-emitter/sensor pair  60  is mounted to the inner frame  30 , as shown in  FIG. 5 . In order to provide an edge  26 , a slot  24  is made on the outer frame  20  and the reflection surface  70  is provided near the edge  26 . Moreover, it is understood by a person skilled in the art that the photo-emitter/sensor pair  60  is operatively connected to a power supply for providing electrical power to the photo-emitter  62  and to an output measurement device  260  so that the output signal from the photo-sensor  64  can be measured for determining the relative movement between the photo-emitter/sensor pair  60  pair and the reflection surface  70 . 
         [0038]    The measured output signal from the photo-sensor  64 , in terms of collector current as a function of movement distance, is shown in  FIG. 6 . As shown, a near-linear range of approximately 1 mm can be found in the middle of curve. Within this range, the measurable movement in the order of few microns is attainable. 
         [0039]    It should be appreciated by a person skilled in the art that the edge  32 ,  36  and  26  as depicted in  FIGS. 3   a  to  5  is part of a frame surface that is substantially perpendicular to the reflection surface. However, the angle between the frame surface and the reflection surface is not necessarily a right angle. The angle can be larger than 90 degrees or smaller than 90 degrees, so long as the part of the light beam from the photo-emitter  62  falling beyond the edge does not yield a significant amount of detectable light as compared to the reflected light from the reflection surface. Furthermore, in  FIGS. 3   b  and  4 , the width of the reflection surface  70  is greater than the diameter of the light cone  162  on the reflection surface. However, the width w of the reflection surface  70  can be equal to or smaller than the diameter D of the light cone  162  on the reflection surface, as shown in  FIG. 7 . Moreover, the reflection surface  70  can also be a wedge-shaped surface, as shown in  FIG. 8 . 
         [0040]    In a different embodiment of the present invention, two separate optical sensors are used on one motion axis to form a differential position system. As shown in  FIG. 9 , a photo-emitter/sensor pair  60  has a photo-emitter  62  for projecting a light cone  162  on a reflection surface  70 , and a photo-sensor  64  for sensing the amount light reflected by the reflection surface  70 . A separate photo-emitter/sensor pair  60 ′ has a photo-emitter  62 ′ for projecting a light cone  162 ′ on a different reflection surface  70 ′, and a photo-sensor  64 ′ for sensing the amount of light reflected by the reflection surface  70 ′. As shown in  FIG. 9 , the reflection surface  70  is provided near an edge  32  of the frame  30 , and the reflection surface  70 ′ is provided near another edge  32 ′ of the same frame  30 . The distance between the photo-emitter pair  60  and the photo-emitter pair  60 ′ is fixed so that when the position signal of one photo-emitter/sensor pair is increased due to the relative movement between frame  30  and the photo-emitter pairs, the position signal of the other photo-emitter pair is decreased. As such, the final position signal is the difference of the two separate position signals. With the arrangement as shown in  FIG. 9 , external influences such as temperature changes can be substantially eliminated. Furthermore, the effect of mechanical tilting is reduced. 
         [0041]    The position sensing method and system, according to the present invention, can also be used in an imaging system where a reflection surface, such as a prism or a mirror, is used to fold the optical axis of the imaging system. The reflection surface can also be rotated to shift the image projected on the image plane for image stabilization purposes. As shown in  FIG. 10 , the imaging system  300  comprises a system body  310  for housing an image sensor  350  located on the image plane  302 , a front lens or window  320 , a triangular prism  330  and possibly a plurality of other lens elements  340 . When a user uses the imaging system  300  to take pictures, the user&#39;s hand may involuntarily shake, causing the mobile phone to rotate around the Y-axis in a pitch motion, and to rotate around the Z-axis in a yaw motion. These motions may introduce a motion blur to an image being exposed on the image sensor  350 . 
         [0042]    In order to compensate for the pitch and yaw motions during the exposure time, an optical image stabilizer is used. The optical image stabilizer comprises two movement means, such as motors or actuators for causing the prism to rotate around two axes. The rotation axes of the prism are shown in  FIG. 11 . As shown in  FIG. 11 , the prism  330  has two triangular faces  338 ,  339  substantially parallel to the Z-X plane, a base  336  substantially parallel to the X-Y plane, a front face  332  substantially parallel to the Y-Z plane and a back face  334  making a 45 degree angle to the base  336 . In order to reduce the motion blur, the prism may be caused to rotate around the Z-axis and the Y-axis. 
         [0043]    As known in the art, when light enters the prism from its front face  332  in a direction parallel to the X-axis, the light beam is reflected by total internal reflection (TIR) at the back face  334  toward the image sensor  330 . 
         [0044]    The tilting of the prism can be achieved by using a gimballed joint  400  to mount the prism  330  for rotation at pivot  430  and pivot  440 , as shown in  FIG. 12 . The gimballed joint  400  is rotatably mounted on a mount  420  which is fixedly mounted to the system body  310  of the imaging system (see  FIG. 10 ). The gimballed joint  400  has a frame  410  operatively connected to the pivot  430  for rotation about the Z-axis relative to the mount  420 . A prism mount  450 , which is used to carry the prism  330 , is rotatably mounted on the frame  410  at pivot  440  so as to allow the prism to rotate about the Y-axis. In order to sense the position of the prism relative to the system body  310 , a photo-emitter/sensor pair  460  is used to sense the position of a surface  412  of the frame  410  and another photo-emitter/sensor  460 ′ is used to sense the position of the prism mount  450 . 
         [0045]    As shown in  FIG. 13 , the surface  412  has an aperture or slot  414  to provide an edge  416  near a reflection surface  470  so as to allow the photo-emitter/sensor pair  460  to sense the relative movement of the surface  412  relative to the mount  420 . Likewise, a reflection surface  470 ′ is provided on the surface of the prism mount  450  near an edge  452  so as to allow the photo-emitter/sensor pair  460 ′ to sensor the relative movement of the prism mount  450  relative to the frame  410 . 
         [0046]    It should be noted that optical sensors such as photo-emitter/sensor pairs are low-end components and, thus, the performance variation is generally quite large. It would be advantageous and desirable to calibrate the position system during start-up of the optical image stabilizer. This can be done by driving the moving member (lens, image sensor) over the entire available motion range, for example. During this stroke, the sensor output is measured at both extremes of the motion range. When the output signals at the two extremes are known, all the intermediate positions can be accurately determined from the intermediate output signals. 
         [0047]    Although the invention has been described with respect to one or more embodiments thereof, it will be understood by those skilled in the art that the foregoing and various other changes, omissions and deviations in the form and detail thereof may be made without departing from the scope of this invention.