Abstract:
Drive unit that consists of two or more strings that are with one end attached to a shaft of a driving motor, and with the other end directly or indirectly coupled to an image capturing device, which is supported by means that allow rotation is disclosed. The twisting strings produce a pulling force on the ends of the strings, which generates a motion of the image capturing device. The invented drive unit does not use gears, belts, pulleys or the like, which reduces the weight, lowers the generated noise, and reduces the parts costs. The invented drive unit including the control unit achieves wide range of motion performances ranging from precise positioning to fast motion, including performance equivalent to a human eye.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    Japanese patent application: appl. (21) JP 2014-032653 (Feb. 24, 2014) 
       BACKGROUND OF THE INVENTION 
       [0002]    (1) Field of the Invention 
         [0003]    The present invention relates to drive units for image capturing devices and control method thereof. The invented drive unit generates motion of the image capturing device or multiple image capturing devices by using twisted strings mechanism. 
         [0004]    (2) Description of Related Art 
         [0005]    Image capturing devices such as semiconductor cameras are used for surveillance and for robotic eyes, particularly in humanoid robots. Image capturing devices are immovably fixed to the base or are movable with the goal to increase visibility range of the device. Motion of the device can be generated by various types of motors that are directly coupled to the device (for example U.S. Pat. No. 6,628,338 B1) or coupled by gear and/or link mechanisms (for example U.S. Pat. No. 7,777,810 B2). 
         [0006]    Particularly in the case of robotic eyes, fast motion of the image capturing device is needed to achieve motion that is similar to a human or live being&#39;s eye. A large torque is needed to realize fast motion, therefore, in the case of directly coupled motors, the motors become large and thus heavy. On the other hand, in the case of gear reducers used with the motor, the weight and size of the motors can be reduced, but the mechanisms generate noise, and the motion appearance is “too mechanical” to be suitable for humanoid robots, which should resemble eye motion of a live being. 
         [0007]    What is still needed, is a drive unit for image capturing device that achieves motion performance similar to a human eye, that is, maximum angular speed of 900 angular degrees per second, operates quietly, is of small size and lightweight, and resembles motion of an eye of a live being. 
       BRIEF SUMMARY OF THE INVENTION 
       [0008]    A drive unit of the present invention is composed of two or more strings that are with one end attached to a shaft of a driving motor, and with the other end directly or indirectly coupled to an image capturing device, which is supported by means that allow rotation. Rotation of the shaft of the driving motor twists the strings on each other. Twisting strings produce a pulling force on the ends of the strings, which generates a motion of the image capturing device. The rotation of the motor shaft is by the invented drive unit transmitted into rotation of the image capturing device. 
         [0009]    The twisted strings function similarly to a muscle of a live being, that is, they generate a pulling force, and cannot push on the image capturing device. When returning motion of the image capturing device is needed, the strings are unwound, and motion of the image capturing device into returning direction is generated by another pair of strings or by a spring that is attached to the image capturing device in such a way that pulls or pushes into the direction opposite to the pulling of the twisted strings. 
         [0010]    Additionally, the rotation of the motor shaft is controlled by a control unit, which uses external commands and a feedback signal in a form of detected rotational angle of the image capturing device or uses information from image processing of the image obtained from the image capturing device. 
         [0011]    Moreover, in the case when two image capturing devices (semiconductor cameras in general) are used as a pair of robotic eyes or as a pair of cameras to obtain a three dimensional view, the invented drive units are used to drive each image capturing device separately or both simultaneously in a pan (left-right) direction, and each image capturing device separately or both simultaneously in a tilt (up-down) direction. 
         [0012]    The invented drive unit does not use gears, belts, pulleys or the like, which reduces the weight, lowers the generated noise, and reduces the parts costs. The invented drive unit including the control unit achieves wide range of motion performances ranging from precise positioning to fast motion, including performance equivalent to a human eye, namely maximum rotational speed of 900 angular degrees per second. 
         [0013]    Additional aspects and advantages of the invention will be apparent from the detailed description of preferred embodiments thereof with reference to the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]    The accompanying drawings show embodiments of the invention of which 
           [0015]      FIG. 1  is an isometric view of a drive unit in accordance with the invention; 
           [0016]      FIG. 2  is an isometric view of embodiment in accordance with the invention where two drive units are implemented to drive an image capturing device in two separate directions; 
           [0017]      FIG. 3  is a view of another embodiment of the invention where two drive units are implemented to drive an image capturing device in two separate directions; 
           [0018]      FIG. 4  is a view of embodiment in accordance with the invention where two drive units are implemented as antagonistic pair; 
           [0019]      FIG. 5  is an isometric view of embodiment in accordance with the invention where two drive units are implemented to drive two separate image capturing devices; 
           [0020]      FIG. 6  is an isometric view of embodiment in accordance with the invention where two drive units are implemented to drive two separate image capturing devices independently in pan direction, and one drive unit to drive two image capturing units simultaneously in tilt direction; 
           [0021]      FIG. 7  is a block diagram of control system in accordance with the invention to control the invented drive unit; 
           [0022]      FIG. 8  is another block diagram of control system in accordance with the invention to control the invented drive unit. 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0023]      FIG. 1  shows an isometric view of a drive unit where two or more strings  3  are with one end attached to a shaft  5  of a driving motor  4 , and with the other end are coupled to a member  2 , which is fixed to the image capturing device  1 , and supports the image capturing device  1  so that it can rotate around its vertical axis. Rotation of the shaft  5  twists the strings  3  and thus generates a pulling force on the member  2 , which rotates together with the image capturing device  1  around its vertical axis. A spring  6  is directly or indirectly attached to the image capturing device  1  in such a way that generates a motion of the image capturing device  1  in opposite direction to the pulling direction of the twisted strings  3 . The twisted strings  3  and the spring  6  thus operate as an antagonistic pair on the image capturing device  1 , with a function to rotate the image capturing device  1  around its vertical axis in both directions. 
         [0024]      FIG. 2  shows an image capturing device  1  attached by a member  2  to a frame  8 , so that the image capturing device  1  can freely rotate around its vertical axis in the frame  8 . The frame  8  is supported by means not shown in the figure in such a way that the frame  8  can freely rotate around its horizontal axis. Two or more strings  3  are with one end attached to a shaft  5  of a driving motor  4  and with the other end are coupled to a member  7 , which is fixed to the image capturing device  1 . Rotation of the shaft  5  twists the strings  3  and thus generates a pulling force on the member  7 , which rotates together with the image capturing device  1  around its vertical axis. A spring  6  is attached to the member  7  in such a way that generates a force opposite to the pulling force of the twisted strings  3 . Further on, two or more strings  9  are with one end attached to a shaft  11  of a second driving motor  10 , and with the other end are coupled directly or indirectly to the frame  8 . Rotation of the shaft  11  twists the strings  9  and thus generates a pulling force on the frame  8 , which rotates together with the image capturing device  1  around its horizontal axis. A spring  12  is attached to the frame  8  in such a way that it generates a force opposing to the pulling force of the twisted strings  9 . The twisted strings  3  and the spring  6 , and the twisted strings  9  and the spring  12  both separately operate as antagonistic pairs to rotate the image capturing device  1  around its vertical axis and around its horizontal axis in both directions independently. 
         [0025]      FIG. 3  shows another embodiment of driving unit of  FIG. 2  where the twisted strings  3  and  9  are both attached to the member  7 , and the spring  6  is also coupled to the member  7 . This arrangement contributes to reduced number of parts needed to drive the image capturing device  1  around its horizontal and around its vertical axes independently. 
         [0026]      FIG. 4  shows yet another embodiment of driving unit of  FIG. 2  where the twisted strings  3  and  9  are both attached to a member  2  in such a way that they operate as an antagonistic pair to rotate the image capturing device  1  around its horizontal axis, and simultaneously both operate as an antagonistic pair with the spring  6  to rotate the image capturing device  1  around its vertical axis. Namely, when the strings  3  are twisting and the strings  9  are untwisting, the pulling force on the member  2  works in such a way that the image capturing device  1  is in the frame  8  rotated around its horizontal axis to tilt down, and oppositely, when the strings  3  are untwisting and the strings  9  are twisting, the pulling force on the member  2  works in such a way that the image capturing device  1  in the frame  8  rotates around its horizontal axis to tilt up. On the other hand, when the strings  3  and the strings  9  are both twisting, the pulling force on the member  2  works in such a way that the image capturing device  1  is together with the frame  8  rotated around its vertical axis to pan right, and oppositely, when the strings  3  and the strings  9  are both untwisting, the pulling force on the frame  8  by the spring  6  works in such a way that the image capturing device  1  is together with the frame  8  rotated around its vertical axis to pan left. In this embodiment the motors are aligned in the direction behind the image capturing axis of the image capturing device contributing a favorable configuration for assembly into a robotic head. 
         [0027]      FIG. 5  shows an isometric view of embodiment where two or more strings  3  are with one end attached to a shaft  5  of a driving motor  4 , and with the other end are coupled to a member  2 , which is fixed to the image capturing device  1 , and supports the image capturing device  1  so that it can rotate around its vertical axis. Rotation of the shaft  5  twists the strings  3  and thus generates a pulling force on the member  2 , which rotates together with the image capturing device  1  around its vertical axis. A spring  6  is directly or indirectly coupled to the image capturing device  1  in such a way that generates a motion of the image capturing device  1  in opposite direction to the pulling direction of the twisted strings  3 . The twisted strings  3  and the spring  6  thus operate as an antagonistic pair on the image capturing device  1 , with a function to rotate it around its vertical axis in both directions. Additionally two or more strings  23  are with one end attached to a shaft  25  of a driving motor  24 , and with the other end are coupled to a member  22 , which is fixed to the second image capturing device  21 , and supports the second image capturing device  21  so that it can rotate around its vertical axis. Rotation of the shaft  25  twists the strings  23  and thus generates a pulling force on the member  22 , which rotates together with the second image capturing device  21  around its vertical axis. The spring  6  is directly or indirectly coupled to the image capturing device  21  in such a way that generates a motion of the second image capturing device  21  in opposite direction to the pulling direction of the twisted strings  23 . The twisted strings  23  and the spring  6  thus operate as an antagonistic pair on the image capturing device  21 , with a function to rotate it around its vertical axis in both directions. The spring  6  in this embodiment is coupled to both image capturing devices, and as such contributes to reduced fluctuations of the spring force in the case of stereo camera or robotic eyes, where the two image capturing devices  11  and  21  both mostly pan (rotate left and right) for the same amount of angle. 
         [0028]      FIG. 6  shows an isometric view of embodiment where two or more strings  3  are with one end attached to a shaft  5  of a driving motor  4 , and with the other end are coupled to a member  2 , which is fixed to the image capturing device  1 , and supports the image capturing device  1  so that it can rotate around its vertical axis. Rotation of the shaft  5  twists the strings  3  and thus generates a pulling force on the member  2 , which rotates together with the image capturing device  1  around its vertical axis. A spring  6  is directly or indirectly attached to the image capturing device  1  in such a way that generates a motion of the image capturing device  1  in opposite direction to the pulling direction of the twisted strings  3 . The twisted strings  3  and the spring  6  thus operate as an antagonistic pair on the image capturing device  1 , with a function to rotate it around its vertical axis in both directions. Additionally two or more strings  23  are with one end attached to a shaft  25  of a driving motor  24 , and with the other end are coupled to a member  22 , which is fixed to the second image capturing device  21 , and supports the second image capturing device  21  so that it can rotate around its vertical axis. Rotation of the shaft  25  twists the strings  23  and thus generates a pulling force on the member  22 , which rotates together with the second image capturing device  21  around its vertical axis. The spring  6  is directly or indirectly attached to the image capturing device  21  in such a way that generates a motion of the second image capturing device  21  in opposite direction to the pulling direction of the twisted strings  23 . The twisted strings  23  and the spring  6  thus operate as an antagonistic pair on the image capturing device  21 , with a function to rotate it around its vertical axis in both directions. The spring  6  in this embodiment is coupled to both image capturing devices, and as such contributes to reduced fluctuations of the spring force in the case of stereo camera or robotic eyes, where the two image capturing devices  11  and  21  both mostly pan (rotate left and right) for the same amount of angle. Additionally, the image capturing devices  1  and  21  are both by their respective members  2  and  22  attached to a common frame  8 , which is supported by means not shown in the figure in such a way that the frame  8  can freely rotate around its horizontal axis. Two or more strings  9  are with one end attached to a shaft  11  of a driving motor  10  and with the other end are coupled to the frame  8 . 
         [0029]    Rotation of the shaft  11  twists the strings  9  and thus generates a pulling force on the frame  8  in such a way that frame  8  rotates and with it rotate both image capturing devices  1  and  21  around their horizontal axes. A spring  12  is attached to the frame  8  in such a way that generates a force opposite to the pulling force of the twisted strings  9 . The twisted strings  9  and the spring  12  operate as an antagonistic pair to rotate the frame  8  and with it both image capturing devices  1  and  21  around horizontal axis in both directions. 
         [0030]    A block diagram of control system to control drive unit is shown in  FIG. 7 , where drive unit for image capturing device  31  has detection means of camera angle or speed  32 , and detection means of motor angle or speed  33 . The control computing unit  37  receives external motion command  36 , and by using image capturing device&#39;s angle or speed  34  and motor angle or speed  35 , calculates according to control algorithm a needed signed voltage  38 , which is transmitted to the driving motor in the drive unit for image capturing device  31  to achieve desired motion performance. 
         [0031]      FIG. 8  shows another embodiment of control system to control drive unit of  FIG. 7  where image processing means  41  are used to obtain image capturing device&#39;s angle or speed  34 . This arrangement contributes to reduced number of parts needed to control the driving unit, because the image capturing device&#39;s angle or speed etc. are obtained from an image processing of the signal from the image capturing device, thus the detection means of camera angle or speed are not separately needed. 
         [0032]    The invention is not limited to the above embodiments and various modifications may be made without departing from the spirit and scope of the invention. Any improvement may be made in part or all of the components.