Patent Publication Number: US-2016227119-A1

Title: Optical image stabilizer and camera module including the same

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the benefit under 35 USC 119(a) of Korean Patent Application No. 10-2015-0014027 filed on Jan. 29, 2015, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference. 
     BACKGROUND 
     1. Field 
     The following description relates to an optical image stabilizer and a camera module including the same. 
     2. Description of Related Art 
     Recently, camera modules have been mounted in mobile devices. Such camera modules commonly include a lens, a lens barrel, an integrated circuit (IC) driving the lens. Since camera modules mounted in mobile devices such as smartphones have a lens aperture smaller than that of a general camera, an amount of light entering a camera module mounted in a mobile device is less than that of a general camera at the time of capturing an image. Therefore, camera modules mounted in mobile devices commonly have relatively slow shutter speeds in order to compensate for an insufficient amount of light. However, blurring of an image is generated even with a small amount of hand-shake, such that it may be difficult to obtain a clear image with such a camera module. 
     Research into technology for various types of optical image stabilizers (OISs), for instance, the OIS of Korean Patent No. 10-2014-0088310, has been conducted in an attempt to solve the problem of blurring of images generated due to the hand-shake or movement of a device. 
     SUMMARY 
     This Summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This Summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter. 
     In one general aspect, a camera module including an optical image stabilizer in which a stopped state is reliably determined. The optical image stabilizer includes an angular velocity calculator configured to receive an angular velocity signal from an angular velocity sensor and output a corrected angular velocity signal generated by correcting the angular velocity signal and an angular position signal; a state detector configured to calculate an amount of energy by summing squared values of the corrected angular velocity signal during an energy period, comparing the amount of energy with a threshold value to determine a stopped state or a moving state of a camera module, and output a corrected angular position signal and control coefficients; and a lens controller configured to control a lens module according to the corrected angular position signal and the control coefficients. 
     In another general aspect, a camera module includes an angular velocity calculator configured receive an angular velocity signal from an angular velocity sensor and output a corrected angular velocity signal and an angular position signal; a state detector configured to calculate an amount of energy by summing squared values of the corrected angular velocity signal during an energy period, comparing the amount of energy with a threshold value to determine a stopped state or a moving state of the camera module, and outputting a corrected angular position signal and control coefficients; a lens controller configured to output a control signal according to the corrected angular position signal and the control coefficients; and a lens module configured to adjust a position of a lens barrel according to the control signal. 
     Other features and aspects will be apparent from the following detailed description, the drawings, and the claims. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a block diagram illustrating an example of a camera module; 
         FIG. 2  is a block diagram illustrating an example of an angular velocity calculator of the camera module of  FIG. 1 ; 
         FIG. 3A  is a graph illustrating an example of an angular velocity signal over time when a state of the camera module is changed from a stopped state to a moving state. 
         FIG. 3B  is a graph illustrating an example of an amount of energy over time, calculated on the basis of a angular velocity signal when a state of the camera module is changed from a stopped state to a moving state. 
         FIG. 4A  is a graph illustrating an example of an angular position signal when a state of the camera module is changed from a moving state to a stopped state. 
         FIG. 4B  is a graph illustrating an example of a corrected angular position signal when a state of the camera module is changed from a moving state to a stopped state. 
         FIG. 5A  is a graph illustrating an example of an angular position signal over time, and a corrected angular position signal over time, when a state of the camera module is changed from a stopped state to a moving state. 
         FIG. 5B  is a graph illustrating an example of an angular position signal over time, and a corrected angular position signal over time, when a state of the camera module is changed from a stopped state to a moving state. 
         FIG. 6A  is a graph illustrating an example of an angular velocity signal over time, when a state of the camera module is changed from a torque receiving state to a stopped state. 
         FIG. 6B  is a graph illustrating an example of a corrected angular position signal when a state of the camera module is changed from a torque receiving state to a stopped state. 
         FIG. 6C  is a graph illustrating an example of a corrected angular position signal by a clipping operation of the camera module when a state of the camera module is changed from a torque receiving state to a stopped state. 
     
    
    
     Throughout the drawings and the detailed description, the same reference numerals refer to the same elements. The drawings may not be to scale, and the relative size, proportions, and depiction of elements in the drawings may be exaggerated for clarity, illustration, and convenience. 
     DETAILED DESCRIPTION 
     The following detailed description is provided to assist the reader in gaining a comprehensive understanding of the methods, apparatuses, and/or systems described herein. However, various changes, modifications, and equivalents of the methods, apparatuses, and/or systems described herein will be apparent to one of ordinary skill in the art. The sequences of operations described herein are merely examples, and are not limited to those set forth herein, but may be changed as will be apparent to one of ordinary skill in the art, with the exception of operations necessarily occurring in a certain order. Also, descriptions of functions and constructions that are well known to one of ordinary skill in the art may be omitted for increased clarity and conciseness. 
     The features described herein may be embodied in different forms, and are not to be construed as being limited to the examples described herein. Rather, the examples described herein have been provided so that this disclosure will be thorough and complete, and will convey the full scope of the disclosure to one of ordinary skill in the art. 
     Referring to  FIG. 1 , the camera module includes an angular velocity sensor  100 , an optical image stabilizer  200 , and a lens module  300 . The optical image stabilizer  200  includes an angular velocity calculator  210 , a state detector  220 , and a lens controller  230 . In addition, the lens module  300  includes a lens driver  310  and a hall sensor  320 . 
     The angular velocity sensor  100  detects an angular velocity and output an angular velocity signal Xo to the optical image stabilizer  200 . In detail, the angular velocity sensor  100  is a sensor that detects shaking of a mobile device or a camera. The angular velocity sensor  100  may be a two-axis gyro sensor, or a three-axis gyro sensor, to detect angular velocity of movement. 
     The angular velocity calculator  210  receives an output from the angular velocity sensor  100  and outputs an angular position signal Po generated by integrating the angular velocity signal Xo. Additionally, the angular velocity calculator  210  performs a correction of the angular velocity signal Xo in order to remove accumulated errors (hereinafter, referred to as “drift”) included in the angular velocity signal Xo due to a noise component during detection of a rotation angle by the angular velocity sensor  100 . 
     The angular velocity calculator  210  integrates a corrected angular velocity signal X(n) generated by correcting the angular velocity signal Xo, thereby calculating the angular position signal Po. That is, the angular velocity calculator  210  outputs, to the state detector  220 , the corrected angular velocity signal X(n) from which the noise component has been removed and the angular position signal Po generated by integrating the corrected angular velocity signal X(n). 
     The state detector  220  calculates an amount of energy on the basis of the corrected angular velocity signal X(n) and compares the amount of energy with a threshold value to determine a stopped state of the camera module. Here, the amount of energy (Em) is calculated by squaring the corrected angular velocity signal X(n) and summing squared values of the corrected angular velocity signal X(n) during an energy period. 
     The calculated amount of energy (Em) described above is represented by the following Equation 1: 
     
       
         
           
             
               
                 
                   Em 
                   = 
                   
                     
                       ∑ 
                       
                         n 
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                   [ 
                   
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     Here, T is the number of corrected angular velocity signals X(n) sampled during a single time period (that is, the energy period) in which the amount of energy is summed. The energy period is set in consideration of a sampling rate of the angular velocity signal, the characteristics of the angular velocity sensor, and a design for improving reliability in stopped state determination. 
     In addition, the state detector  220  performs low-pass-filtering of the corrected angular velocity signal X(n) and calculates the amount of energy on the basis of the low-pass-filtered corrected angular velocity signal. To this end, the state detector  220  includes a low pass filter disposed at an input terminal thereof to which the corrected angular velocity signal X(n) is input. The low pass filter improves a signal-to-noise ratio (SNR) of the corrected angular velocity signal X(n) to enable determination of the stopped state of the camera module by the amount of energy (Em), without calibrating a threshold value for the lens module  300 . 
     After the state detector  220  calculates the amount of energy (Em), the state detector  220  compares the amount of energy (Em) with the threshold value and determines whether the camera module is in a stopped state, where the amount of energy (Em) is equal to or less than the threshold value during a first determination period. Then, the state detector  220  outputs a corrected angular position signal Pc and a control coefficient Coef depending on the stopped state determination. 
     When the camera module is determined to be in the stopped state, the state detector  220  gradually decreases the corrected angular position signal Pc and the control coefficients Coef to values corresponding to a zero point (for example, 0) in the stopped state and output the values. 
     Therefore, in the optical image stabilizer and the camera module including the same, a delay time required for outputting the angular position signal generated by correcting and integrating the angular velocity signal as the value corresponding to the zero point in the stopped state is significantly decreased. 
     After the state detector  220  calculates the amount of energy (Em), the state detector  220  compares the amount of energy (Em) with the threshold value and determines that the camera module is in a moving state if the amount of energy (Em) is equal to or greater than the threshold value during a second determination period. When the camera module is in the moving state, the state detector  220  outputs the corrected angular position signal Pc to follow the angular position signal Po during a following time, and output the corrected angular position signal Pc having the same level as the angular position signal Po after the following time. 
     Therefore, in the optical image stabilizer of the camera module, an image jump phenomenon, generated when immediately outputting the corrected angular position signal Pc having the same level as the angular position signal P at the time of determining the moving state of the camera module, is prevented. 
     The lens controller  230  receives the corrected angular position signal Pc and the control coefficient Coef and outputs a control signal to the lens module  300 . In addition, the lens controller  230  receives feedback information output by the lens module  300  in order to calculate corrected positional information according to the feedback information and reflect the corrected positional information in the control signal. The control coefficient Coef may be a plurality of control coefficients for a proportional integral derivative (PID) controller included in the lens controller  230 . 
     The lens driver  310  included in the lens module  300  receives the control signal to adjust a position of a lens barrel (not illustrated) supporting a lens or a lens group. The lens driver  310  may comprise a voice coil motor (VCM) using electromagnetic force of a coil and a magnet, an ultrasonic motor using a piezoelectric element, a shape memory alloy, or any combination thereof. 
     The hall sensor  320  detects positional information of the lens, supported by the lens barrel and moved by the lens driver  310 , and outputs this as feedback information. Since there is a limitation on a range of positions of the lens or the lens barrel (not illustrated) that may be adjusted by the lens driver  310 , an upper limit and a lower limit of the corrected angular position signal Pc input from the state detector  220  to the lens controller  230  sets a clipping range. 
     Referring to  FIG. 2 , the angular velocity calculator  210  includes an offset remover  211 , a filter  212 , and an integrator  213 . 
     The offset remover  211  and the filter  212  perform the correction of the angular velocity signal Xo in order to remove drift included in the angular velocity signal Xo due to the noise component during detection of the rotation angle by the angular velocity sensor  100  (see  FIG. 1 ). Since the noise component is indicated by a specific frequency, the filter  212  may include a high pass filter in order to remove the noise component. The high pass filter is a digital filter, and may be an infinite impulse response (IIR) filter filtering by recursively applying an input signal and an output signal. A transfer function (that is, H(z)) of the IIR filter may derived as represented by the following Equation 2: 
     
       
         
           
             
               
                 
                   
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                   [ 
                   
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                   ] 
                 
               
             
           
         
       
     
     Here, state coefficients (b 0  to b N  and a 1  to a M ) of the IIR filter are input depending on characteristics of a filter that is to be modeled in advance. 
     When drift is generated due to accumulation of the noise component at the time of detecting the rotation angle by the angular velocity sensor  100  (see  FIG. 1 ), a significant amount of time (for example, several tens of seconds) may be required for the filter  212  to remove this noise component. Therefore, the offset remover  211  removes an offset from the angular velocity signal Xo as preprocessing for filtering. 
     Although when the corrected angular velocity signal X(n) is branched from an output of the offset remover  211  and is then output to the state detector  220  is illustrated in  FIG. 2 , the corrected angular velocity signal X(n) is branched from an output of the filter  212  and then output to the state detector  220 . 
     The integrator  213  integrates the angular velocity signal output by the filter  212  and output the angular position signal Po to the state detector  213 . 
     Referring to  FIGS. 3A and 3B , a change in the angular velocity signal, according to camera module movement, is reflected in the amount of energy, and thus, an amount of energy equal to or greater than a threshold value is calculated. 
     Referring to  FIG. 4A , a significant amount of time Td is required from a point in time at which the state of the camera module is changed from the moving state to the stopped state to a point in time at which the angular position signal is output as a value corresponding to a zero point in the stopped state. 
     Referring to  FIG. 4B , the optical image stabilizer determines a point in time T2 as the stopped state of the camera module while the amount of energy equal to or less than the threshold value is continued for a first determination period from a point in time T1 at which the amount of energy equal to or less than the threshold value is sensed, and outputs a value corresponding to a zero point in the stopped state at a predetermined point in time T3 by gradually decreasing the angular position signal (in relation to an absolute value) to the value corresponding to the zero point in the stopped state (for example, 0). Therefore, in the optical image stabilizer, the zero point is rapidly corrected depending on the determination of the stopped state. 
     Referring to  FIGS. 1, 5A and 5B , a predetermined time is required from a point in time Ms at which the moving state of the camera module is reflected in the angular position signal up to time Md of determining the moving state of the camera module. 
     The state detector  220  (see  FIG. 1 ) of the optical image stabilizer outputs the corrected angular position signal Pc to follow the angular position signal Po during a predetermined following time, and outputs the corrected angular position signal Pc having the same level as the angular position signal Po after the following time. 
     Therefore, the image jump phenomenon due to an amount of change A in the corrected angular position signal Pc generated in a case of immediately outputting the corrected angular position signal Pc having the same level as the angular position signal P at the time Md of determining the moving state of the camera module is prevented. 
     Referring to  FIGS. 6A and 6B , since an upper limit and a lower limit of the corrected angular position signal input from the state detector  220  (see  FIG. 1 ) to the lens controller  230  sets a clipping range, the corrected angular position signal is not output along dotted lines, but is output while having a predetermined upper limit. However, a long transient response is present from a point in time at which the state of the camera module is changed from the torque receiving state to the stopped state to a point in time at which the corrected angular position signal is output as a value (for example, 0) corresponding to a zero point in the stopped state. The transient response allows a user to experience a freezing phenomenon in which the lens does not remain at a position corresponding to the zero point, but is positioned at a boundary, and prevents hand-shake correction from being performed. 
     Referring to  FIGS. 6A and 6C , when the state detector  220  (see  FIG. 1 ) determines that the camera module is in the moving state and the angular position signal reaches the clipping range, the state detector  220  stores state values of the filter  212  (see  FIG. 2 ) and the integrator  213  (see  FIG. 2 ) in a register. Here, the state value of the filter is an internal memory value of the digital filter included in the filter, and the state value of the integrator is an internal memory value of the integrator and an integrated angular velocity signal output from the integrator. 
     In addition, the state detector  220  compares a previous angular position signal with a current angular position signal. The state detector determines that the previous angular position signal reaches a maximum value (M2) when the current angular position signal is reduced to be lower than the previous angular velocity signal. When the angular position signal reaches the maximum value, the state detector  220  applies (M3) the stored state values to the filter and the integrator. Therefore, the transient response may be cancelled, and the corrected angular position signal reaches the value (for example, 0) corresponding to the zero point in the stopped state more quickly. As set forth above, in the optical image stabilizer, the stopped state is reliably and quickly determined. 
     The apparatuses, and other components, such as the angular velocity calculator, the lens controller, the state detector, the lens driver, the hall sensor, the angular velocity sensor, the offset remover, the filter, the integrator, and state detector illustrated in  FIGS. 1 and 2 , that perform the operations described herein with respect to  FIGS. 3-6C  are implemented by hardware components. Examples of hardware components include controllers, sensors, generators, drivers, memories, comparators, arithmetic logic units, adders, subtractors, multipliers, dividers, integrators, and any other electronic components known to one of ordinary skill in the art. In one example, the hardware components are implemented by computing hardware, for example, by one or more processors or computers. A processor or computer is implemented by one or more processing elements, such as an array of logic gates, a controller and an arithmetic logic unit, a digital signal processor, a microcomputer, a programmable logic controller, a field-programmable gate array, a programmable logic array, a microprocessor, or any other device or combination of devices known to one of ordinary skill in the art that is capable of responding to and executing instructions in a defined manner to achieve a desired result. In one example, a processor or computer includes, or is connected to, one or more memories storing instructions or software that are executed by the processor or computer. Hardware components implemented by a processor or computer execute instructions or software, such as an operating system (OS) and one or more software applications that run on the OS, to perform the operations described herein. The hardware components also access, manipulate, process, create, and store data in response to execution of the instructions or software. For simplicity, the singular term “processor” or “computer” may be used in the description of the examples described herein, but in other examples multiple processors or computers are used, or a processor or computer includes multiple processing elements, or multiple types of processing elements, or both. In one example, a hardware component includes multiple processors, and in another example, a hardware component includes a processor and a controller. A hardware component has any one or more of different processing configurations, examples of which include a single processor, independent processors, parallel processors, single-instruction single-data (SISD) multiprocessing, single-instruction multiple-data (SIMD) multiprocessing, multiple-instruction single-data (MISD) multiprocessing, and multiple-instruction multiple-data (MIMD) multiprocessing. 
     Instructions or software to control a processor or computer to implement the hardware components and perform the methods as described above are written as computer programs, code segments, instructions or any combination thereof, for individually or collectively instructing or configuring the processor or computer to operate as a machine or special-purpose computer to perform the operations performed by the hardware components and the methods as described above. In one example, the instructions or software include machine code that is directly executed by the processor or computer, such as machine code produced by a compiler. In another example, the instructions or software include higher-level code that is executed by the processor or computer using an interpreter. Programmers of ordinary skill in the art can readily write the instructions or software based on the block diagrams and the flow charts illustrated in the drawings and the corresponding descriptions in the specification, which disclose algorithms for performing the operations performed by the hardware components and the methods as described above. 
     The instructions or software to control a processor or computer to implement the hardware components and perform the methods as described above, and any associated data, data files, and data structures, are recorded, stored, or fixed in or on one or more non-transitory computer-readable storage media. Examples of a non-transitory computer-readable storage medium include read-only memory (ROM), random-access memory (RAM), flash memory, CD-ROMs, CD-Rs, CD+Rs, CD-RWs, 
     CD+RWs, DVD-ROMs, DVD-Rs, DVD+Rs, DVD-RWs, DVD+RWs, DVD-RAMs, BD-ROMs, BD-Rs, BD-R LTHs, BD-REs, magnetic tapes, floppy disks, magneto-optical data storage devices, optical data storage devices, hard disks, solid-state disks, and any device known to one of ordinary skill in the art that is capable of storing the instructions or software and any associated data, data files, and data structures in a non-transitory manner and providing the instructions or software and any associated data, data files, and data structures to a processor or computer so that the processor or computer can execute the instructions. In one example, the instructions or software and any associated data, data files, and data structures are distributed over network-coupled computer systems so that the instructions and software and any associated data, data files, and data structures are stored, accessed, and executed in a distributed fashion by the processor or computer. 
     While this disclosure includes specific examples, it will be apparent to one of ordinary skill in the art that various changes in form and details may be made in these examples without departing from the spirit and scope of the claims and their equivalents. 
     The examples described herein are to be considered in a descriptive sense only, and not for purposes of limitation. Descriptions of features or aspects in each example are to be considered as being applicable to similar features or aspects in other examples. Suitable results may be achieved if the described techniques are performed in a different order, and/or if components in a described system, architecture, device, or circuit are combined in a different manner, and/or replaced or supplemented by other components or their equivalents. Therefore, the scope of the disclosure is defined not by the detailed description, but by the claims and their equivalents, and all variations within the scope of the claims and their equivalents are to be construed as being included in the disclosure.