Abstract:
A stepper motor is controlled by a driver having a constant and maximum frequency input in order to correct for camera shake. The need for variable frequency devices is eliminated, thereby reducing the cost and complexity of the system.

Description:
TECHNICAL FIELD 
     This invention relates to imaging systems, and more specifically, to an improved method for controlling an image stabilizer in a digital image capture system. 
     BACKGROUND OF THE INVENTION 
     Imaging systems can create blurry or unreadable images if the camera system shakes while the image is being captured. This is particularly problematic in digital symbol reading systems, where it is important to correctly capture a digital image containing data to be decoded. An example of such systems are those used to read 2-dimensional bar codes. 
     Many systems have long existed for attempting to correct this problem. These systems typically compensate by moving a detection array, such as a charge coupled device (CCD) in response to movements of the camera system. Other prior systems move the camera lens in response to shaking to compensate for movement of the camera. 
     A typical prior art such compensation system is shown in  FIG. 1 . In operation, if the camera shakes, summer  108  will output a signal representing the rate of change of the camera position with respect to time. Integrator  109  then generates a signal X representing the change in position of the camera. This signal X controls a compensator  110 , which in turn is fed back through amplifier  101  for control of variable frequency (“V/F”) converter  102 . 
     That output frequency of V/F converter  102  is fed to driver  103  which controls the stepping motor  104  in a manner that is proportional to the frequency output by V/F converter  103 . The stepping motor  104  then controls camera module  105 , which includes an image sensor and a gyroscope sensor  107  as shown. The signal from stepping motor  104  moves the image sensor to correct for the camera shake. Thus, due to the feedback loop shown, the greater the amplitude of the camera shake, the greater the correction will be. 
     While the above system provides reasonable performance, one problem with it is that the V/F converter is a relatively expensive and complicated component to manufacture and control. Accordingly, the system is more costly than it needs to be, and is also subject to failures. The output frequency must track an input error signal relatively accurately. 
     In view of the above, there exists a need in the art for a more efficient and simpler design to compensate for camera shake in a digital imaging system. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  depicts a prior art camera shake compensation circuit; and 
         FIG. 2  shows an exemplary embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       FIG. 2  depicts an exemplary embodiment of the present invention comprising a driver  202 , which is driven by a constant and predetermined maximum frequency. An exemplary value of such a frequency in a typical system would be 2 kHz. The stepping motor  203  operates at a constant speed, but the driver  202  can change the direction of the stepping motor  203  based upon the input to the driver  202 . In operation, and similar to prior arrangements, the degree of camera shake is determined by integrator  205  and compensator  206 . However, rather than utilizing a variable frequency device, such as in prior systems, the comparator  201  simply puts out a plus or minus which causes driver  201  to move stepping motor  203  at predetermined amounts in the selected direction. Of course, the driver can also cause the stepping motor to remain stationary during any one or more clock cycles. 
     Since the maximum frequency is used at driver  202 , the output of driver  202  is sufficient to move the stepping motor  203  quickly enough to compensate for camera shake. In short, the input to stepping motor  203  does not vary in value, but instead may only be one of three values, either a fixed positive value, a fixed negative value or 0. The fixed positive and negative values are preferably the same value with opposite signs, but may also have different magnitudes. 
     As a result of the foregoing, the need for the variable frequency converter  102  of the prior art may be eliminated, and the operation of the device simplified. 
     It is noted that while the gyro sensor and other components are shown as examples, the invention is not limited by such examples. The stepping motor may be replaced with other position control mechanisms and/or motors, and each of the integrator and compensator may be implemented in either hardware or in software. Additionally, while it is preferred that the clock pulse for driver  202  be set at the frequency required to implement the fastest practical correction for camera shake, the clock pulse may be set at a slightly lower frequency. Also, the comparison measurements may be taken every clock cycle, or every Nth clock cycle, where N is an integer greater than 1. 
     It is also noted that while the foregoing explanation is with respect to correction of camera shake in one dimension, there are actually three dimensions which need correction. Accordingly, the same configuration of stepping motors and drivers can be independently implemented in three different dimensions, and readily combined to correct for total camera shake. This also allows the frequency and fixed amount of movement for the stepper motors to be different in different directions. Additionally, the stepper motor may correct for shake by moving one or more of the camera module, a Charge Coupled Device (CCD) or similar device within the camera module, or a lens. Further, the amount of movement and frequencies utilized for the driver  202  may be different for each dimension of camera shake. Also, the prior art variable frequency generator can be used for correction in one dimension, while the fixed frequency device described above can be used for correction in another direction, although such an embodiment is less preferred. 
     Additionally, the lens, the CCD, or the entire camera module may be moved in response to the output of comparator  201 . 
     These and other variations are intended to be covered by the following claims.