Automatic focus imaging system using out-of-plane translation of an MEMS reflective surface

The present invention provides an automatic focus imaging system comprising a lens unit, an image sensor, and a Micro-Electro-Mechanical System (MEMS) unit fabricated by microfabrication technology to improve the portability and focusing speed of the automatic focus imaging system. The MEMS unit for automatic focusing comprises a substrate having a control circuitry, at least one reflective surface movably connected to the substrate, and at least one actuation unit comprising a micro-actuator having a large in-plane translation and at least one micro-converter configured to convert the large in-plane translation of the micro-actuator to the large out-of-plane translation of the reflective surface. The MEMS unit changes a distance between lens unit and the image sensor by controlling the out-of-plane translation of the reflective surface in order to form an in-focus image on the image sensor.

FIELD OF INVENTION

The present invention relates to an automatic focus imaging system and, more particularly to a reliable, fast, light weight, compact, low power consumption automatic focus imaging system using out-of-plane translation of a micro-electro-mechanical system reflective surface.

BACKGROUND OF THE INVENTION

The invention contrives to provide a reliable, fast, light weight, compact, low power consumption automatic focusing system for portable devices such as cellular phone camera.

As the position of an object changes, a focus distance representing a distance between a lens and a plane that a focused image of the object is formed also changes. To form the focused image of the object on the image sensor automatically, a sensor distance representing a distance between the lens and the image sensor has to be the same as the focus distance. The focus distance or the sensor distance can be defined in various ways depending on the optical arrangements of optical elements. In the conventional automatic focus systems, the sensor distance is matched with the focus distance by moving one or more optical elements such as lens, mirror and sensor. The majority of the conventional automatic focus imaging systems perform automatic focus by moving one or more lenses equipped with electro-magnetically driven motors and/or piezo-electrically actuated apparatus. Since the lens or lenses in those systems have a considerable inertia and need to have macroscopic mechanical motions, the automatic focus imaging systems require a macroscopic actuator generating large actuating force. The macroscopic actuator can pose many problems including low focusing speed and low portability due to the increase of volume, mass and power consumption. Alternatively, the automatic focus can be performed by using a movable sensor. But, it also requires a macroscopic actuator with additional complexity to satisfy electrical connection. For simpler automatic focus, a movable mirror can be used. While the movable mirror can provide a simple and reliable automatic focus, it still requires a macroscopic actuator such as voice coil.

To apply the automatic focus imaging system to portable devices such as cellular phone camera, it is very important to reduce the volume, mass and power consumption of the automatic focus imaging system and increase the reliability and speed of automatic focus function.

SUMMARY OF THE INVENTION

The present invention contrives to improve the focusing speed and portability of an automatic focus imaging system by reducing volume, mass and/or power consumption of the system.FIG. 1shows a conventional automatic focus imaging system using the translation of a reflective surface. An actuator is connected to the reflective surface such that the reflective surface moves to adjust focus. Since the optical system with automatic focusing function requires additional optical components including a reflective surface and an actuator, the optical system has larger volume and mass than an optical system without automatic focusing function. To apply automatic focus imaging system to portable devices such as cellular phone camera, it is very important to reduce the volume, mass and power consumption of the automatic focus imaging system and increase the reliability and focusing speed of automatic focusing function.

In the present invention, the automatic focusing function is performed by a Micro-Electro-Mechanical System (MEMS) unit. The MEMS unit has a small volume and mass and low power consumption, and its operation is very reliable, precise, and fast. The MEMS unit for automatic focus includes at least one reflective surface and at least one actuation unit fabricated on the same substrate by microfabrication technology. By fabricating the reflective surface and the actuation unit on the same substrate, the volume, mass and power consumption of the automatic focus imaging system of the present invention can be greatly reduced, which increases the portability and focusing speed of the automatic focus imaging system. In general, an actuator used for automatic focusing is required to provide several hundreds micrometer of out-of-plane translation to a reflective surface. The out-of-plane translation is defined as a translation in the surface normal direction of the substrate while the in-plane translation is defined as a translation in the direction of an axis laying on the substrate surface. The conventional MEMS devices are capable of providing out-of-plane translation to the reflective surface and have an advantage of adding negligible volume and mass to the optical system. However, they have a limited range in the out-of-plane translation (typically only several micrometers) while having a large range in the in-plane translation. In order to increase the range of the out-of-plane translation, the actuation unit of the present invention preferably comprises at least one micro-actuator and at least one micro-converter, wherein the micro-converter converts the in-plane translation of the micro-actuator to out-of-plane translation of the reflective surface. The micro-converter of the present invention allows large out-of-plane translation by converting the large in-plane translation of the micro-actuator into the large out-of-plane translation of the reflective surface. Preferably, the micro-actuator is actuated by electrostatic force. The micro-actuator can be a least one comb-drive using electrostatic force. The comb-drive can generate “coming and going” in-plane motion with a short stroke. The combination of two comb-drives can be used as a micro-actuator, wherein two comb-drives generate in-plane revolution and the in-plane revolution is converted to large linear in-plane translation. Then, the large linear in-plane translation can be converted to the large out-of-plane translation by the micro-converter. The micro-converter comprises at least one primary end, which can be connected to the micro-actuator or the substrate. All structures in the MEMS unit including the reflective surface, micro-actuator, and the micro-converter can be fabricated on the same substrate by microfabrication technology and the micro-actuator can be controlled by applied voltage.

An automatic focus imaging system of the present invention comprises a lens unit, an image sensor and an MEMS unit fabricated by microfabrication technology to improve the portability and focusing speed of the automatic focus imaging system. The MEMS unit comprises a substrate having a control circuitry, a reflective surface movably connected to the substrate, and at least one actuation unit. The actuation unit comprises a micro-actuator disposed on the substrate and driven by the control circuitry to have in-plane translation and at least one micro-converter having a primary end, wherein the primary end of at least one of the at least one micro-converter is rotatably connected to the micro-actuator and the micro-actuator with the in-plane translation exerts a force on the primary end of the at least one of the at least one micro-converter. The at least one micro-converter delivers the force to the reflective surface so that the reflective surface has a motion comprising out-of-plane translation motion. The MEMS unit changes a distance between lens unit and the image sensor by controlling the out-of-plane translation of the reflective surface in order to form an in-focus image on the image sensor.

In one embodiment of the present invention, at least one of the at least one micro-converter can comprise a first beam and a second beam, wherein a first end of the first beam is the primary end of the at least one micro-converter and a second end of the first beam is rotatably connected to the reflective surface, wherein a first end of the second beam is rotatably connected to the reflective surface and a second end of the second beam is rotatably connected to the substrate.

In another embodiment of the present invention, at least one of the at least one micro-converter can comprise a first beam and a second beam, wherein a first end of the first beam is the primary end of the at least one micro-converter and a second end of the first beam is rotatably connected to a first end of the second beam, wherein a second end of the second beam is rotatably connected to the substrate, wherein the reflective surface is pushed by a pivot point connecting the second end of the first beam and the first end of the second beam in order to have the motion.

In still another embodiment of the present invention, at least one of the at least one micro-converter can comprise at least one beam, wherein a first end of the beam is the primary end of the at least one micro-converter and a second end of the beam is rotatably connected to the reflective surface.

At least one of the at least one micro-converter is rotatably connected to the reflective surface.

At least one of the at least one micro-converter is rotatably connected to the substrate.

The reflective surface is pushed by at least one of the at least one micro-converter in order to have the motion.

In order to provide better support and precise positioning, the actuation unit can comprise a plurality of the micro-converters. In one embodiment of the present invention, the primary ends of the plurality of the at least on micro-converters are rotatably connected to the micro-actuator and the micro-actuator with the in-plane translation exerts the forces on the primary ends of the plurality of the at least one micro-converters. Then, the at least one micro-converter delivers the forces to the reflective surface so that the reflective surface has a motion comprising out-of-plane translation motion. In another embodiment, while the primary end of at least one of the at least one micro-converter is rotatably connected to the micro-actuator, the primary end of at least another one of the at least one micro-converter can be configured to slide on the substrate. In still another embodiment of the present invention, while the primary end of at least one of the at least one micro-converter is rotatably connected to the micro-actuator, the primary end of at least another one of the at least one micro-converter can be configured to roll on the substrate. In still another embodiment of the present invention, while the primary end of at least one of the at least one micro-converter is rotatably connected to the micro-actuator, the primary end of at least another one of the at least one micro-converter can be configured to be rotatably connected to the substrate.

The MEMS unit can further comprise at least one flexible member connecting the reflective surface and the substrate and providing restoring force to the reflective surface.

The automatic focus imaging system can further comprises a beam splitter positioned between the lens unit and the MEMS unit. Alternatively, the reflective surface can be obliquely positioned between the lens unit and the image sensor such that the reflective surface reflects light received from the lens unit to the image sensor.

The automatic focus imaging system can further comprise a focus status determination unit in communication with the control circuit to provide focus status to the control circuitry in order to automatically control the out-of-plane translation of the reflective surface. The focus status determination unit can comprise at least one distance measurement sensor providing distance information between the imaging system and an object and generating a-signal for the control circuitry to automatically control the out-of-plane translation of the reflective surface. In another way, the focus status determination unit comprises a focus detection sensor capturing at least a portion of image to determine the focus status and generating a signal for the control circuitry to automatically control the out-of-plane translation of the reflective surface. Alternatively, the focus status determination unit comprises an image processor in communication with the image sensor and the control circuit, wherein the image processor uses an algorithm to compare image quality of an image data from the image sensor with focus criteria and generates a signal for the control circuitry to automatically control the out-of-plane translation of the reflective surface.

The micro-actuator is actuated by electrostatic force. The micro-actuator can be a comb-drive.

The MEMS unit can comprises a plurality of the at least one actuation units. In this case, each of the micro-actuators in the plurality of the at least one actuation units can be driven independently by the control circuitry. The motion of the reflective surface further comprises rotation, wherein the micro-actuators driven independently control the rotation of the reflective surface.

The focus (or image) can be shifted by the out-of-plane translations of the reflective surfaces. The reflective surface is configured to be rotated to compensate focus shift with respect to the image sensor. The rotation of the reflective surface can be controlled to compensate focus shift with respect to the image sensor. The automatic focus imaging system can further comprise an image processor configured to generate a signal for the control circuitry to automatically control rotation of the reflective surface to compensate focus shift with respect to the image sensor by using a compensation algorithm.

The reflective surface is flat. Also, the reflective surface is curved.

The reflective surface can be a mirror or a micromirror. Also, the reflective surface can be a reflective membrane.

The portable optical devices have a high demand to provide high quality images while maintaining compactness. When the automatic focus imaging system uses a single reflective surface having a large area size, distortion and twisting problems of the reflective surface can occur, which causes aberration. The present invention provides more robust and reliable automatic focus imaging system using a plurality of reflective surfaces. The automatic focus imaging system comprises a lens unit, an image sensor and MEMS unit fabricated by microfabrication technology to improve the portability and focusing speed of the automatic focus imaging system. The MEMS unit comprises a substrate having a control circuitry, a plurality of reflective surfaces movably connected to the substrate, and at least one actuation unit. The actuation unit comprises a micro-actuator disposed on the substrate and driven by the control circuitry to have in-plane translation and at least one micro-converter having a primary end. The primary end of at least one of the at least one micro-converter is rotatably connected to the micro-actuator and the micro-actuator with the in-plane translation exerts a force on the primary end of the at least one of the at least one micro-converter, wherein the at least one micro-converter delivers the force to the plurality of reflective surfaces so that each of the plurality of reflective surfaces has a motion comprising out-of-plane translation motion. The MEMS unit is configured to change a distance between lens unit and the image sensor by controlling the out-of-plane translation of each of the plurality of reflective surfaces in order to form an in-focus image on the image sensor. The automatic focus imaging system of the present invention can have more robust and reliable automatic focusing function by using a plurality of reflective surfaces.

In the present invention, the fabrication thickness of the reflective surface can be less than 100 μm. Also, the fabrication thicknesses of the micro-actuator and the micro-converter can be less than 100 μm.

The reflective surface can be configured to translate at least 100 μm. Also, the reflective surface can be configured to translate between 50 μm and 1,000 μm.

Although the present invention is brief summarized herein, the full understanding of the invention can be obtained by the following drawings, detailed description, and appended claims.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1shows a conventional automatic focus imaging system using a mirror translation. The conventional automatic focus imaging system11uses a mirror12configured to be actuated by a macroscopic actuator13. This automatic focus imaging system can pose many problems including bulky size, large power consumption, low focusing speed, and eventually decrease in portability.

FIG. 2is a schematic diagram of one preferred embodiment of an automatic focus imaging system using an MEMS unit of the present invention. The automatic focus imaging system21comprises a lens unit22, an image sensor23, and an MEMS unit24. Although the lens unit in figures is illustrated as a single objective lens, those skilled in the art will understand that the lens unit may comprise a plurality of lenses depending upon a particular application. The MEMS unit24comprises a substrate25having a control circuitry (not shown), a least one reflective surface26movably connected to the substrate25, and at least one actuation unit27disposed on the substrate25and configured to be driven by the control circuitry to move the reflective surface26. The MEMS unit24changes a distance between lens unit22and the image sensor23by controlling the out-of-plane translation TO of the reflective surface26in order to form an in-focus image on the image sensor23. The MEMS unit24is fabricated by microfabrication technology to improve the portability and focusing speed of the automatic focus imaging system21. Since the out-of-plane dimension of the reflective surface26and the actuation unit27is typically in order of several micrometers, the volume and mass of the MEMS unit24is negligible. Also, due to its low inertia, the MEMS unit has very fast response time and low power consumption. Therefore, the automatic focus imaging system21of the present invention has greatly improved portability and focusing time compared to conventional automatic focus imaging systems using a macroscopic actuator. The automatic focus imaging system21can further comprise a beam splitter28in order for the reflective surface26to reflect incident light22A into the image sensor23. When the beam splitter28is used as shown in this configuration, the sensor distance representing a distance between the lens unit22and the image sensor23can be defined as a sum of distances a, b and c, wherein the distances a, b and c denote a distance between the lens unit22and the reflective surface26, a distance between the reflective surface26and the beam splitter28, and a distance between the beam splitter28and the image sensor23, respectively. Also, a focus distance representing a distance between the lens unit22and a plane that a focused image of the object is formed is defined as a sum of distances a, b and d (not shown), wherein the distances a, b, and d denote a distance between the lens unit22and the reflective surface26, a distance between the reflective surface26and the beam splitter28, and a distance between the beam splitter28and the plane that the focused image of the object is formed, respectively. To form the focused image of the object on the image sensor automatically, the sensor distance has to be matched with the focus distance. In the present invention, the sensor distance is matched with the focus distance by controlling the out-of-plane translation TO of the reflective surface26, wherein the distance a (the distance between the lens unit22and the reflective surface26) and the distance b (the distance between the reflective surface26and the beam splitter28) are changed. Although the sensor distance and the focus distance are defined for a particular example ofFIG. 2, those skilled in the art will understand that the sensor distance and the focus distance can be defined differently based on the geometric arrangement of the optical elements.

In some cases, it is desirable to position the reflective surface26obliquely with respect to an optical axis of the lens unit22instead of using the beam splitter28since the beam splitter28typically wastes 75% of the incident light22A.FIG. 3is a schematic diagram for another preferred embodiment of an automatic focus imaging system using an obliquely positioned MEMS unit. The automatic focus imaging system31comprises a lens unit32, an image sensor33, and an MEMS unit34. The MEMS unit34comprises a substrate35having a control circuitry, at least one reflective surface36movably connected to the substrate35, and at least one actuation unit37disposed on the substrate35and configured to be driven by the control circuitry to move the reflective surface36. The MEMS unit34is obliquely positioned between the lens unit32and the image sensor33and configured to automatically focus an image received from the lens unit32to the image sensor33by controlling the out-of-plane translation TO of the reflective surface36using the actuation unit37. The out-of-plane translation TO of the reflective surface36is controlled by the actuation unit37driven by the control circuitry to change a distance between the lens unit32and the image sensor33in order to form in-focus image on the image sensor33. The sensor distance representing a distance between the lens unit32and the image sensor33in this configuration can be defined as a sum of distances a and e, wherein the distances a and e denote a distance between the lens unit32and the reflective surface36and a distance between the reflective surface36and the image sensor33, respectively. Also, a focus distance representing a distance between the lens unit32and a plane that a focused image of the object is formed is defined as a sum of distances a and f (not shown), wherein the distances a and d denote a distance between the lens unit32and the reflective surface36and a distance between the reflective surface36and the plane that the focused image of the object is formed, respectively. To form the focused image of the object on the image sensor33automatically, the sensor distance has to be matched with the focus distance. In the present invention, the sensor distance is matched with the focus distance by controlling the out-of-plane translation TO of the reflective surface36, wherein the distance a (the distance between the lens unit32and the reflective surface36) and the distance f (the distance between the reflective surface36and the image sensor33) are changed.

FIGS. 4A-4Hare schematic diagrams of side views of various preferred embodiments of an MEMS unit configured to generate the large out-of-plane translation of a reflective surface for automatic focusing. The conventional MEMS devices are capable of providing a limited range of out-of-plane translation (typically only several micrometers), while a range of the in-plane translation can be more than several millimeters. To provide the large out-of-plane translation of the reflective surface, the present invention uses a micro-actuator having a large in-plane translation and a micro-converter configured to convert the large in-plane translation of the micro-actuator to a large out-of-plane translation of the reflective surface. The MEMS unit41comprises a substrate42having a control circuitry, at least one reflective surface43movably connected to the substrate42, and at least one actuation unit44(or44A,44B).

The actuation unit44comprises a micro-actuator45(or45A,45B) disposed on the substrate42and driven by the control circuitry to have in-plane translation D (or DA, DB) and at least one micro-converter46(or46A,46B) having a primary end. At least one of the at least one micro-converter46is coupled to the micro-actuator45, wherein the primary end of the at least one of the at least one micro-converter46is rotatably connected to the micro-actuator45so that the micro-actuator45with the in-plane translation D can exert a force on the primary end of the at least one of the at least one micro-converter46. When the actuation unit44comprises two or more micro-converters, all the micro-converters can have the same structure. Alternatively, at least one of the micro-converters can have a different structure from other micro-converters. When the actuation unit44comprises two or more micro-converters46and the primary end of the at least one of the micro-converters46is rotatably connected to the micro-actuator45, the primary end of at least another one of the micro-converters46can be configured to slide, roll, or be rotatably connected on the substrate42. When the micro-actuator45exerts the force on the primary end of the at least one of the at least one micro-converter46, the at least one micro-converter delivers the force to the reflective surface43so that the reflective surface43has a motion comprising out-of-plane translation TO.

The micro-actuator45having the in-plane translation D can be a comb-drive. The reflective surface43can be made to have various motions by designing the micro-converter46accordingly depending on applications. The at least one micro-converter46can be configured to convert the in-plane translation D of the micro-actuator45to a motion of the reflective surface43. The at least one micro-converter46can be configured to convert the in-plane translation D of the micro-actuator45to the out-of-plane translation TO of the reflective surface43. The at least one micro-converters46can be configured to convert the in-plane translation D of the micro-actuator45to the translation and rotation of the reflective surface43, wherein the translation of the reflective surface43includes in-plane translation TI and the out-of-plane TO. The at least one micro-converter46is configured to convert the in-plane translation D of the micro-actuator45to the rotation and out-of-plane translation of the reflective surface43.

FIGS. 4A,4B,4D, and4I show MEMS units comprising an actuation unit, whileFIGS. 4C,4E-4H show MEMS units comprising a plurality of actuation units.

FIG. 4Ashows an MEMS unit41having an actuation unit44, wherein the actuation unit44comprises a micro-actuator45disposed on the substrate42and driven by the control circuitry to have in-plane translation D and a micro-converter46having a primary end. The micro-converter46comprises a first beam B1and a second beam B2. A first end of the first beam B1is the primary end and a second end of the first beam B1is rotatably connected to the reflective surface43. A first end of the second beam B2is rotatably connected to the reflective surface43and a second end of the second beam B2is rotatably connected to the substrate42. The primary end of the micro-converter46is rotatably connected to the micro-actuator45. The micro-actuator45with the in-plane translation D exerts a force to the primary end of the first beam B1of the micro-converter46and induces the translations and rotations of the beams B1, B2. The translating and rotating beams B1, B2make the reflective surface43have a motion comprising out-of-plane translation TO. The out-of-plane translation TO of the reflective surface43can be precisely controlled by the actuation unit44driven by the control circuitry in order to form in-focus image on the image sensor. In addition to the out-of-plane translation TO of the reflective surface43, the in-plane translation D of the micro-actuator45can make the reflective surface43have in-plane translation TI as shown inFIG. 4A. The MEMS unit41ofFIG. 4Acan further comprises at least one flexible member (not shown) connecting the reflective surface43and the substrate42and providing restoring force to the reflective surface43.

When the MEMS unit uses a single actuation unit with a single micro-converter, the reflective surface has a single supporting point or area, which can cause the distortion and twisting problems for the reflective surface with a large area resulting in aberration. To resolve this problem, the MEMS unit can be configured to provide a plurality of supporting points or areas for the reflective surface as shown inFIGS. 4B-4I.FIG. 4Bshows an MEMS unit41having at least one actuation unit44, wherein the actuation unit44comprises a micro-actuator45disposed on the substrate42and configured to have in-plane translation D and a plurality of micro-converters46A,46B having a primary end and configured to convert the in-plane translation D of the micro-actuator45to the motion of the reflective surface43. Each of the micro-converters46A,46B comprises a first beam BA1, BB1and a second beam BA2, BB2, respectively. A first end of the first beam BA1, BB1is the primary end and a second end of the first beam BA1, BB1is rotatably connected to the reflective surface43, respectively. A first end of the second beam BA2, BB2is rotatably connected to the reflective surface43and a second end of the second beams BA2, BB2is rotatably connected to the substrate42, respectively. The primary end of at least one of the plurality of micro-converters46A,46B is rotatably connected to the micro-actuator45.FIG. 4Bshows the exemplary MEMS unit41comprising two micro-converters46A,46B, wherein both primary ends of the micro-converters46A,46B are rotatably connected to the micro-actuator45. The micro-actuator45with the in-plane translation D exerts a force on both primary ends of the micro-converters46A,46B and induces the translations and rotations of the beams BA1, BA2, BB1, BB2. The translating and rotating beams BA1, BA2, BB1, BB2make the reflective surface43have a motion comprising out-of-plane translation TO. The out-of-plane translation TO of the reflective surface43can be precisely controlled by the actuation unit44driven by the control circuitry in order to form in-focus image on the image sensor. In addition to the out-of-plane translation TO of the reflective surface43, the in-plane translation D of the micro-actuator45can make the reflective surface43have in-plane translation TI as shown inFIG. 4B. The MEMS unit41ofFIG. 4Bcan further comprises at least one flexible member (not shown) configured to connect the reflective surface43and the substrate42and providing restoring force to the reflective surface43. By using a plurality of micro-converters46A,46B, the actuation unit44can provide better support for the reflective surface43and control the motion of the reflective surface43more precisely. In addition, since a single micro-actuator45can provide a uniform in-plane translation D for the micro-converters46A,46B, the unwanted tilt of the reflective surface43can be prevented.

FIG. 4Bshows the case that both primary ends of the micro-converters are connected to the micro-actuator. Alternatively, the primary end of one micro-converter can be rotatably connected to the micro-actuator while the primary end of another micro-converter is configured to slide, roll, or be rotatably connected on the substrate. The micro-actuator with the in-plane translation exerts a force on the primary end of the one micro-converter and induces the translations and rotations of the beams of both micro-converters. The translating and rotating beams make the reflective surface have a motion comprising out-of-plane translation.

FIG. 4Cshows an MEMS unit41having a plurality of actuation units44A,44B, wherein each of the actuation units44A,44B comprises a micro-actuator45A,45B disposed on the substrate42and configured to have in-plane translation DA, DB and at least one micro-converter46A,46B comprising a primary end and configured to convert the in-plane translation DA, DB of the micro-actuator45A,45B to the motion of the reflective surface43, respectively. The micro-converter46A,46B in each of the actuation units44A,44B comprises a first beam BA1, BB1and a second beam BA2, BB2, respectively. In each of the micro-converters46A,46B, a first end of the first beam BA1, BB1is the primary end and a second end of the first beam BA1, BB1is rotatably connected to the reflective surface43, respectively. Also, a first end of the second beams BA2, BB2is rotatably connected to the reflective surface43and a second end of the second beam BA2, BB2is rotatably connected to the substrate42, respectively. The primary ends of the micro-converters46A,46B are rotatably connected to the micro-actuators45A,45B, respectively. The micro-actuators45A,45B with the in-plane translation DA, DB exert forces to the primary ends of the first beams BA1, BB1of the micro-converters46A,46B, respectively and induce the translations and rotations of the beams BA1, BA2, BB1, BB2. The translating and rotating beams BA1, BA2, BB1, BB2make the reflective surface43have a motion comprising out-of-plane translation TO. The out-of-plane translation TO of the reflective surface43can be precisely controlled by the actuation units44A,44B driven by the control circuitry in order to form in-focus image on the image sensor. In addition to the out-of-plane translation TO of the reflective surface43, the in-plane translations DA, DB of the micro-actuators45A,45B can make the reflective surface43have in-plane translation TI as shown inFIG. 4C. The MEMS unit41ofFIG. 4Ccan further comprises at least one flexible member (not shown) configured to connect the reflective surface43and the substrate42and providing restoring force to the reflective surface43. The plurality of actuation units44can provide better support for the reflective surface43and control the motion of the reflective surface43more precisely.

FIG. 4Dshows an MEMS unit41having at least one actuation unit44, wherein the actuation unit44comprises a micro-actuator45disposed on the substrate42and configured to have in-plane translation D and a plurality of micro-converters46A,46B comprising a primary end and configured to convert the in-plane translation D of the micro-actuator45to the motion of the reflective surface43. Each of the micro-converters46A,46B comprises a first beam BA1, BB1and a second beam BA2, BB2, respectively. A first end of the first beam BA1, BB1in each micro-converter46A,46B is the primary end and a second end of the first beam BA1, BB1is rotatably connected to a first end of the second beam BA2, BB2, respectively. A second end of the second beam BA2, BB2is rotatably connected to the substrate42. The primary ends of the micro-converters46A,46B is rotatably connected to the micro-actuator45. The micro-actuator45with the in-plane translation D exerts a force to the primary ends of the first beams BA1, BB1of the micro-converters46A,46B. In this configuration, the reflective surface43is configured to be pushed by pivot points49A,49B connecting the second ends of the first beams BA1, BB1and the first ends of the second beams BA2, BB2, respectively, in order to have a motion. The MEMS unit41further comprises at least one flexible member47connecting the reflective surface43and the substrate42and providing restoring force to the reflective surface43. Also, the restoring force of the flexible member47makes the pivot points49A,49B of the micro-converters46A,46B be in contact with the bottom of the reflective surface43. The in-plane translation D of the micro-actuators45induces the translations and rotations of the beams BA1, BA2, BB1, BB2. The translating and rotating beams BA1, BA2, BB1, BB2make the reflective surface43have the motion comprising out-of-plane translation TO. The out-of-plane translation TO of the reflective surface43can be precisely controlled by the actuation units44driven by the control circuitry in order to form in-focus image on the image sensor. The MEMS unit41ofFIG. 4Dcan minimize the undesired in-plane translation of the reflective surface43by making the pivot points49A,49B slid and/or roll along the reflective surface43. Since a single micro-actuator45can provide a uniform in-plane translation D for the micro-converters46A,46B, the unwanted tilt of the reflective surface43can be prevented. Also, by using a plurality of micro-converters46A,46B, the actuation unit44can provide better support for the reflective surface43and control the motion of the reflective surface43more precisely.

FIG. 4Eshows an MEMS unit41having a plurality of actuation units44A,44B, wherein each of the actuation units44A,44B comprises a micro-actuator45A,45B disposed on the substrate42and configured to have in-plane translation DA, DB and at least one micro-converter46A,46B comprising a primary end and configured to convert the in-plane translation DA, DB of the micro-actuator45A,45B to the motion of the reflective surface43, respectively. The micro-converter46A,46B in each of the actuation units44A,44B comprises a plurality of beams. Each micro-converter46A,46B in each of the actuation units44A,44B comprises a first beam BA1, BB1and a second beam BA2, BB2, respectively. A first end of the first beam BA1, BB1in each micro-converter46A,46B is the primary end and a second end of the first beam BA1, BB1is rotatably connected to a first end of the second beam BA2, BB2, respectively. A second end of the second beam BA2, BB2is rotatably connected to the substrate42. The primary ends of the micro-converters46A,46B are rotatably connected to the micro-actuators45A,45B, respectively. The micro-actuators45A,45B with the in-plane translation DA, DB exert forces to the primary ends of the first beams BA1, BB1of the micro-converters46A,46B, respectively. In this configuration, the reflective surface43with the motion is configured to be pushed by pivot points49A,49B connecting the second ends of the first beams BA1, BB1and the first ends of the second beams BA2, BB2, respectively, in order to have a motion. The MEMS unit41further comprises at least one flexible member47connecting the reflective surface43and the substrate42and providing restoring force to the reflective surface43. Also, the restoring force of the flexible member47makes the pivot points49A,49B of the micro-converters46A,46B be in contact with the bottom of the reflective surface43. The in-plane translations DA, DB of the micro-actuators45A,45B induce the translations and rotations of the beams BA1, BA2, BB1, BB2and make the reflective surface43have the motion comprising out-of-plane translation TO. The out-of-plane translation TO of the reflective surface43can be precisely controlled by the actuation units44A,44B driven by the control circuitry in order to form in-focus image on the image sensor. The MEMS unit41ofFIG. 4Ecan minimize undesired in-plane translation of the reflective surface43by making the pivot points49A,49B slid or roll along the reflective surface43.

The focus (or image) can be shifted when the out-of-plane translation of the reflective surface is used for automatic focus. In this case, the rotation of the reflective surface can be controlled to compensate focus shift with respect to the image sensor. The MEMS unit of the present invention is capable of providing the reflective surface with rotation as well as out-of-plane translation when the MEMS unit comprises two or more of the actuation units, wherein each actuation unit is configured to be driven independently by control circuitry.FIG. 4Fshows the embodiment ofFIG. 4Eproviding a rotation as well as out-of-plane translation. The out-of-plane translation TO of the reflective surface43is controlled by the actuation units44A,44B driven by the control circuitry in order to form in-focus image on the image sensor and the rotation R of reflective surface43is controlled by the actuation units44A,44B driven by the control circuitry to compensate focus shift with respect to the image sensor. Each actuation unit44A,44B is driven independently by control circuitry.

FIGS. 4G and 4Hshow MEMS units41comprising a plurality of actuation units44A,44B, wherein each of the actuation units44A,44B comprises a micro-actuator45A,45B disposed on the substrate42and configured to have in-plane translation DA, DB and at least one micro-converter46A,46B comprising a primary end and configured to convert the in-plane translation DA, DB of the micro-actuator45A,45B to the motion of the reflective surface43, respectively. Each micro-converter46A,46B in the actuation units44A,44B comprise a beam BA, BB, respectively. A first end of the beam BA, BB in each of the micro-converters46A,46B is the primary end and a second end of the beam BA, BB is rotatably connected to the reflective surface43, respectively. The primary ends of the micro-converters46A,46B are rotatably connected to the micro-actuators45A,45B, respectively. The micro-actuators45A,45B with the in-plane translation DA, DB exert forces to the primary ends of the beams BA, BB of the micro-converters46A,46B, respectively. The in-plane translations DA, DB of the micro-actuator45A,45B induce the translations and rotations of the beams BA, BB and make the reflective surface43have a motion comprising out-of-plane translation TO. The motion of the reflective surface43can be a pure out-of-plane translation TO without introducing in-plane translation of the reflective surface43.FIG. 4Gshows that the MEMS unit41can provide a pure out-of-plane translation TO for the reflective surface43by controlling the in-plane-translations DA, DB of the micro-actuators45A,45B. The out-of-plane translation TO of the reflective surface43can be precisely controlled by the actuation units44A,44B driven by the control circuitry in order to form in-focus image on the image sensor.

The focus (or image) can be shifted when the out-of-plane translation of the reflective surface is used for automatic focus. In this case, the rotation of the reflective surface can be controlled to compensate focus shift with respect to the image sensor.FIG. 4Hshows the MEMS unit41ofFIG. 4Gproviding the reflective surface43with both out-of-plane translation TO and rotation R, wherein the out-of-plane translation TO of the reflective surface43is controlled by the actuation units44A,44B driven by the control circuitry in order to form in-focus image on the image sensor and the rotation R of reflective surface43is controlled by the actuation units44A,44B driven by the control circuitry to compensate focus shift with respect to the image sensor. Each actuation unit44A,44B can be driven independently by the control circuitry. The MEMS unit41ofFIGS. 4G and 4Hcan further comprises at least one flexible member (not shown) configured to connect the reflective surface43and the substrate42and providing restoring force to the reflective surface43.

At least one micro-converter can have a different structure from the other micro-converter as shown inFIG. 4I.FIG. 4Ishows an MEMS unit41having at least one actuation unit44, wherein the actuation unit44comprises a micro-actuator45disposed on the substrate42and configured to have in-plane translation D and a plurality of micro-converters46A,46B comprising a primary end and configured to convert the in-plane translation D of the micro-actuator45to the motion of the reflective surface43. A first micro-converter46A comprises a first beam BA1and a second beam BA2. A first end of the first beam BA1in the first micro-converter46A is the primary end and a second end of the first beam BA1is rotatably connected to the reflective surface43. A first end of the second beam BA2is rotatably connected to the reflective surface43and a second end of the second beams BA2is rotatably connected to the substrate42. The primary end of the first micro-converter46A is rotatably connected to the micro-actuator45. A second micro-converter46B comprises a beam BB. A first end of the beam BB in the second micro-converter46B is the primary end and a second end of the beam BB is rotatably connected to the reflective surface43. The primary end of the second micro-converter46B is rotatably connected to the substrate42. The micro-actuator45with the in-plane translation D exerts a force to the primary end of the beam BA1of the first micro-converter46A. The in-plane translation D of the micro-actuator45induces the translations and rotations of the beams BA1, BA2, BB. The translating and rotating beams BA1, BA2, BB make the reflective surface43have the motion comprising out-of-plane translation TO. The out-of-plane translation TO of the reflective surface43can be precisely controlled by the actuation unit44driven by the control circuitry in order to form in-focus image on the image sensor. In addition to the out-of-plane translation TO of the reflective surface43, the in-plane translation D of the micro-actuator45can make the reflective surface43have in-plane translation TI as shown inFIG. 4I. The MEMS unit41ofFIG. 4Ican further comprises at least one flexible member (not shown) configured to connect the reflective surface43and the substrate42and providing restoring force to the reflective surface43. By using a plurality of micro-converters46A,46B, the actuation unit44can provide better support for the reflective surface43and control the motion of the reflective surface43more precisely. In addition, since a single micro-actuator45can provide a uniform in-plane translation D for the micro-converters46A,46B, the unwanted tilt of the reflective surface43can be prevented. Furthermore, since the micro-actuator45is connected only to the first micro-converter46A directly, the structure of the MEMS unit41becomes much simpler while still providing a plurality of support points to the reflective surface43.

FIGS. 5A and 5Bare schematic diagrams showing how the automatic focus imaging system inFIG. 3of the present invention performs automatic focus.FIG. 5Ais a schematic diagram of an automatic focus imaging system51using a reflective surface56, wherein the out-of-plane translation TO of the reflective surface56changes the focal plane of the automatic focus imaging system51. The lens unit52makes its focus at a focal point59A without a reflective surface. In order to provide automatic focus, a reflective surface56is disposed obliquely with respect to an optical axis52A between the lens unit52and the image sensor53. The reflective surface56is configured to have a plurality of displacements from the substrate55in the out-of-plane direction. When the reflective surface56is located at a position56A, the focus59B is out of the plane of the image sensor53, wherein a sensor distance is the sum of a1 and e while a focus distance is the sum of a1 and f1. Since the sensor distance is different from the focus distance at the reflective surface position56A, the image on the image sensor is not in-focus. To perform automatic focus, the reflective surface56is moved to another position56B in the out-of-plane direction. Then, the reflective surface56and the lens unit52make a focus59C on another focal plane. The position of the focal plane can be adjusted to be on the plane of the image sensor53by controlling the out-of-plane translation TO of the reflective surface56. The out-of-plane translation TO of the reflective surface56is controlled by the actuation unit driven by the control circuitry. When the focal plane is on the plane of the image sensor53, the automatic focus is accomplished, wherein both of the sensor distance and the focus distance are the same as the sum of a2 and e.

The automatic focus imaging system51can further comprise a focus status determination unit58F in communication with the control circuit on the substrate55to provide focus status to the control circuitry. The focus status determination unit58F can comprise at least one distance measurement sensor providing distance information between the imaging system51and an object and generating a signal for the control circuitry to automatically control the out-of-plane translation TO of the reflective surface56in order to form in-focus image on the image sensor53. Alternatively, the focus status determination unit58F can comprise a focus detection sensor capturing at least a portion of object image to determine the focus status and generating a signal for the control circuitry to automatically control the out-of-plane translation TO of the reflective surface56in order to form in-focus image on the image sensor53. Still as another alternative approach, the focus status determination unit58F can comprise an image processor in communication with the image sensor53and the control circuit, wherein the image processor uses an algorithm to compare image quality of an image data from the image sensor53with focus criteria and generates a signal for the control circuitry to automatically control the out-of-plane translation TO of the reflective surface56in order to form in-focus image on the image sensor53.

The automatic focus imaging system51can further comprise an image processor (not shown) configured to generate a signal for the control circuitry to control rotation of the reflective surface56to compensate focus shift with respect to the image sensor53by using a compensation algorithm.

The reflective surface56is not necessarily aligned with 45 degree to an image side optical axis52A. The angle between reflective surface56and the image side optical axis52A can be varied if the optical geometry permits.

FIG. 5Bis a schematic diagram of an automatic focus imaging system using a curved reflective surface56. Similarly to the reflective surface56inFIG. 5A, the position of the focal plane can be adjusted to be on the plane of the image sensor53by controlling the out-of-plane translation TO of the curved reflective surface56. When the focal plane is on the plane of the image sensor53, the automatic focus is accomplished.

FIG. 6is a schematic diagram showing how automatic focus is performed when object distance is changed. When an object is located at a position69A, the reflective surface66is required to have a certain position66A in the out-of-plane direction to make a focus69D on the plane of the image sensor63, wherein both of a sensor distance and a focus distance are the same as the sum of a1 and e. When the object moves from the point69A to other position69B, the image on the image sensor63is defocused if the reflective surface66does not move. The reflective surface66is controlled to have out-of-plane translation TO from one position66A to another position66B so that the focus69E remains on the plane of the image sensor63, wherein both of the sensor distance and the focus distance are the same as the sum of a2 and e. Without changing the focal length of the lens unit62, the automatic focus imaging system61can make its focus on the plane of the image sensor63.

The focus (or image) can be shifted when the out-of-plane translations of the reflective surface is used for automatic focus as shown inFIGS. 5 and 6. As an example, the automatic focus imaging system inFIG. 6is considered. In the automatic focus imaging system ofFIG. 6, the focus is shifted from69D to69E due to automatic focus. To compensate this focus shift, the reflective surface66is configured to have rotation as well as out-of-plane translation.FIG. 7is a schematic diagram of an automatic focus imaging system performing automatic focus and focus shift compensation. The lens unit72makes its focus79A without a reflective surface. In order to provide automatic focus and focus shift compensation, a reflective surface76is disposed obliquely with respect to an optical axis72A between the lens unit72and an image sensor73. The reflective surface76is configured to have a plurality of displacements from the substrate75in the out-of-plane direction and a plurality of rotations. The reflective surface76has out-of-plane translation TO in order to make its focus on the plane of the image sensor73and has rotation R to compensate focus shift. In this case, the focus is changed from79B to79C. The MEMS unit71of the present invention can provide the reflective surface76with both out-of-plane translation TO and rotation R as shown inFIGS. 4C,4F and4H. The automatic focus imaging system71can further comprise an image processor (not shown) configured to generate a signal for the control circuitry to automatically control the rotation R of the reflective surface76to compensate focus shift with respect to the image sensor73by using a compensation algorithm.

When an automatic focus imaging system uses a single reflective surface having a large area size, the distortion and twisting problems of the reflective surface can occur, which causes aberration. The MEMS unit of the present invention can provide more robust and reliable automatic focus imaging system by using a plurality of reflective surfaces, wherein each reflective surface is configured to provide large out-of-plane translation. The automatic focus imaging system comprises a lens unit, an image sensor, and an MEMS unit. The MEMS unit comprises a substrate having a control circuitry, a plurality of reflective surfaces movably connected to the substrate, and at least one actuation unit. The actuation unit comprises a micro-actuator disposed on the substrate and driven by the control circuitry to have in-plane translation and at least one micro-converter having a primary end. The primary end of at least one of the at least one micro-converter is rotatably connected to the micro-actuator and each of the reflective surfaces is coupled to at least one of the at least one micro-converter, wherein the micro-actuator with the in-plane translation exerts a force on the primary end of the at least one of the at least one micro-converter, wherein the at least one micro-converter delivers the force to the plurality of reflective surfaces so that each of the plurality of reflective surfaces has a motion comprising out-of-plane translation motion. The MEMS unit changes a distance between lens unit and the image sensor by controlling the out-of-plane translation of each of the plurality of reflective surfaces in order to form an in-focus image on the image sensor. The MEMS unit is fabricated by microfabrication technology to make the automatic focus imaging system compact. The actuation unit can have any of configurations shown inFIG. 4.

FIG. 8Ais a schematic diagram of a side view of one exemplary MEMS unit using a plurality of reflective surfaces. The MEMS unit81comprises a substrate having a control circuitry, a plurality of reflective surfaces83movably connected to the substrate, a plurality of micro-actuators85configured to have in-plane translations D, and a plurality of micro-converters86comprising a primary end and configured to convert the in-plane translations D of the micro-actuators85to the motion of the reflective surfaces83. The reflective surfaces83, the micro-actuators85, and the micro-converters86are fabricated by microfabrication technology on the same substrate82in order to improve the portability and focusing speed of the automatic focus imaging system.FIG. 8shows the MEMS unit81using micro-converters46shown inFIG. 4C. In this case, each micro-converter86converts the in-plane translations D of the micro-actuators85to the out-of-plane translation TO of the reflective surfaces83. Although the MEMS unit81comprising a plurality of reflective surfaces83is illustrated by using a plurality of MEMS units41ofFIG. 4C, those skilled in the art will understand that the MEMS unit81using a plurality of reflective surfaces83can be made with any combination of micro-actuators and micro-converters including those used in the MEMS units in theFIGS. 4A-4Idepending upon applications. The micro-actuators85and the micro-converters86that make reflective surfaces83move are disposed over the substrate82such that the motion of each reflective surface does not interfere with the motions of other reflective surfaces.FIGS. 8B and 8Cshow schematic diagrams of top views of exemplary arrangements of the reflective surfaces83, micro-actuators85, and micro-converters86. The point or area89on each reflective surface83can be a connecting pivot point or area ofFIGS. 4A-4Cand4G-4I or a contacting pivot point or area ofFIGS. 4D-4Fbetween the reflective surface83and the micro-converter86.

While the invention has been shown and described with reference to different embodiments thereof, it will be appreciated by those skills in the art that variations in form, detail, compositions and operation may be made without departing from the spirit and scope of the invention as defined by the accompanying claims.