Abstract:
A rotating element control system includes a rotating element rotatably disposed on a main body, a first measuring unit which measures an angular movement of the main body, a driving unit which drives the rotating element, a second measuring unit which measures a rotational speed of the rotating element, a transfer unit which connects the rotating element and the driving unit and transfers a driving force to the rotating element, a motion compensation unit which generates a compensation signal which removes an error component generated by the angular movement of the main body, and a stabilization control unit which controls the driving unit based on the compensation signal and a difference between an input signal and the rotational speed of the rotating element.

Description:
CROSS-REFERENCE TO RELATED PATENT APPLICATIONS 
     This application claims priority from Korean Patent Application No. 10-2011-0094279, filed on Sep. 19, 2011, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference in its entirety. 
     BACKGROUND 
     1. Field 
     Apparatuses and methods consistent with exemplary embodiments relate to a rotating shaft control system, and more particularly, to a rotating shaft control system having an improved degree of accuracy in terms of stability by reducing influence of a rotational motion of a main body transferred to a mechanical system. 
     2. Description of the Related Art 
     A remote control weapon station (RCWS) is a system that enables precise shooting on a target by adjusting a weapon from a remote place to prevent a gunner from being exposed to the outside when performing a battle operation at a near or far distance. The RCWS is mounted on a variety of vehicles such as unmanned vehicles, unmanned armored vehicles, unmanned planes, unmanned patrol boats, etc. 
     Since a gunner located at a remote place from an RCWS performs shooting by adjusting a target shooting point of a weapon, a direction of the weapon of the RCWS needs to be rapidly and accurately controlled. 
     Korean Patent Publication No. 2010-0101915 discloses technology relating to a control system for an RCWS, in which an error signal due to a difference between an output speed and an input speed of a driving unit is used for compensating for a frictional force. However, since the control system considers only a frictional force generated from inside the RCWS, an amount of a motion of a vehicle equipped with the RCWS and driving of a rotating shaft according to a speed command instructed by an operator are not free from influence of various frictional disturbances generated by mechanical constituent elements of the RCWS. 
     SUMMARY 
     One or more exemplary embodiments may overcome the above disadvantages and other disadvantages not described above. However, it is understood that one or more exemplary embodiment are not required to overcome the disadvantages described above, and may not overcome any of the problems described above. 
     One or more exemplary embodiments provide a rotating shaft control system having an improved degree of accuracy in terms of stability by reducing influence of a rotational motion of a main body transferred to a mechanical system. 
     One or more exemplary embodiments also provide a rotating shaft control system having a function to effectively remove an error component generated when a rotational motion of a main body is transferred to a mechanical system. 
     According to an aspect of an exemplary embodiment, a rotating element control system includes a rotating element rotatably disposed on a main body, a first measuring unit for measuring an angular motion of a rotation of the main body, a driving unit which drives the rotating element, a second measuring unit which measures a rotational speed of the rotating element, a transfer unit which connects the rotating element and the driving unit and transfers a driving force to the rotating element, a motion compensation unit which generates a compensation signal which removes an error component generated by the angular acceleration of the main body, and a stabilization control unit which controls the driving unit based on the compensation signal and a difference between a stabilization input signal and the rotating shaft speed sensed by the second sensing unit. 
     The angular acceleration of the main body measured by the first sensing unit can be an angular acceleration, and the transfer unit may transfer the driving force to the rotating element at a gear ratio. The compensation signal may include a compensation torque signal T m  calculated according to an equation T m =−(N−1)J m  α h , to offset an error generated as a rotational force of the main body rotating at the angular acceleration α h  is transferred to the transfer unit having the gear ratio N and the driving unit having the rotational inertia mass J m . 
     The stabilization control unit may include at least of a proportional controller, an integral controller, and a derivative controller. 
     The stabilization control unit may include an integral controller for integrating the difference between the rotational speed of the rotating element and the input signal and a proportional-derivative controller receiving the rotational speed of the rotating element as an input. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other aspects will become more apparent by describing in detail exemplary embodiments thereof with reference to the attached drawings in which: 
         FIG. 1A  is a conceptual view schematically illustrating an operational state of an RCWS having a rotating shaft control system according to an exemplary embodiment; 
         FIG. 1B  is a conceptual view schematically illustrating a motion of the rotating shaft control system of  FIG. 1A  in a yaw direction; 
         FIG. 2  is a perspective view illustrating an example of the RCWS of  FIG. 1A ; 
         FIG. 3  is a block diagram illustrating constituent elements of a rotating shaft control system applied to the RCWS of  FIG. 1A ; 
         FIG. 4  is a perspective view schematically illustrating a structure of mechanical elements of the rotating shaft control system of  FIG. 3 ; 
         FIG. 5  is a view schematically illustrating a mechanical relationship among mechanical elements of  FIG. 4 ; 
         FIG. 6  is a conceptual view schematically illustrating a relationship of mechanical elements of  FIG. 5  by using a physical model; 
         FIG. 7  is a block diagram illustrating a physical model of  FIG. 6 ; 
         FIG. 8  is a block diagram illustrating a stabilization control unit of the rotating shaft control system of  FIG. 1A ; 
         FIG. 9  is a graph showing a degree of stabilization accuracy when a pitch motion having a size of 1 Hz is applied to a main body in the rotating shaft control system of  FIG. 3 ; and 
         FIG. 10  is a graph showing a degree of stabilization accuracy when a pitch motion having a size of 2 Hz is applied to a main body in the rotating shaft control system of  FIG. 3 . 
     
    
    
     DETAILED DESCRIPTION 
     Hereinafter, exemplary embodiments will be described in detail with reference to the attached drawings. Like reference numerals in the drawings denote like elements. 
       FIG. 1A  is a conceptual view schematically illustrating an operational state of a remote control weapon station (RCWS) having a rotating shaft control system according to an exemplary embodiment. Referring to  FIG. 1A , the rotating shaft control system according to the present embodiment is used to control driving of an RCWS  100  and includes a rotating shaft  20  rotatably installed on a main body  400 , a driving unit  30  for driving the rotating shaft  20 , a first sensing unit  15  for sensing an angular acceleration of a rotation of the main body  400 , a second sensing unit  25  for sensing a rotational speed of the rotating shaft  20 , a transfer unit  40  for transferring a driving force by connecting the rotating shaft  20  and the driving unit  30 , and a control unit  50 . 
     Although in  FIG. 1A  the main body  400  where the RCWS  100  is installed is a vehicle, the exemplary embodiments is not limited thereto and the RCWS  100  may be installed on any moving device, for example, a ship, a patrol boat, an unmanned scout robot, etc. 
     Referring to  FIG. 1A , the main body  400  equipped with the RCWS  100  is capable of moving toward a target point A and performing sensing and shooting on the target point A with the rotating shaft  20  of the RCWS  100  rotating at a rotational speed ω L  while the main body  400  is moving. Since the main body  400  rotates at a rotational speed ω h  according to a terrain through which the main body  400  travels, a rotational motion generated by the main body  400  may have an influence on control of the RCWS  100 . 
     Disturbance motions of the main body  400  forming a platform for installing the RCWS  100  may be generally divided into two types: an azimuth or yaw motion and an elevation or pitch motion. A motion related to the rotational speed ω h  in  FIG. 1A  corresponds to an elevation motion. In  FIG. 1A , a rotational motion in only an elevation direction is illustrated for convenience of explanation. 
     In order to measure the rotational speed ω h  related to a motion in the elevation direction, instead of directly attaching a sensor to the main body  400 , sensors installed to control the RCWS  100 , that is, a gyro sensor and an encoder, are used to obtain a signal directly or indirectly indicating a yaw motion and an elevation motion. 
     First, it is simple to obtain an angular speed of a motion of the main body  400  in the elevation direction acting as a disturbance in the elevation (or pitch) direction. That is, a pitch angular speed of a gyro sensor installed on the RCWS  100  is used as it is. 
     In  FIG. 1A , the first sensing unit  15  installed on the RCWS  100  corresponds to a gyro sensor for sensing an angular speed of the main body  400 . The gyro sensor installed on the RCWS  100  can be used because the main body  400  and the RCWS  100  form a single body by using a coupling device such as a bolt. Thus, a pitch disturbance of the main body  400  is the same as a pitch angular speed of the RCWS  100 . Since an angular acceleration α h  of a rotation of the main body  40  is obtained by differentiating an angular speed of the main body  400  sensed by the first sensing unit  15 , the angular acceleration α h  may be obtained by using the first sensing unit  15 . 
     Second, obtaining an angular speed of the main body  400  in a yaw direction acting as a disturbance in the yaw direction is slightly complicated compared to the obtaining of a pitch disturbance. A yaw-direction encoder  15   b  (see  FIG. 1B ) installed on the RCWS  100  may be used to measure an angular speed in the yaw direction. 
       FIG. 1B  is a conceptual view schematically illustrating a motion of the rotating shaft control system of  FIG. 1A  in the yaw direction. In  FIG. 1B , the illustration of some of constituent elements of  FIG. 1A  is omitted for convenience of illustration and only constituent elements related to the motion of the RCWS  100  in the yaw direction are illustrated. 
     The RCWS  100  may be installed to be rotatable in a direction indicated by θ (yaw direction) with respect to the main body  400 . A motion of the RCWS  100  rotating in the direction θ is called a yaw motion. In order to sense a rotational motion of the RCWS  100  in the yaw direction, the yaw-direction encoder  15   b  and a yaw-direction gyro sensor  15   c  may be arranged on the RCWS  100 . The control unit  50  may receive signals from the yaw-direction encoder  15   b  and the yaw-direction gyro sensor  15   c.    
     The main body  400  and the RCWS  100  are not integrally coupled to rotate in the yaw direction. The RCWS  100  is installed to be rotatable in the yaw direction with respect to the main body  400  via a rotation gear (not shown) and a rotation bearing (not shown). Thus, the RCWS  100  and the main body  400  may rotate in different directions. 
     An angular speed in the yaw direction that is a disturbance in the yaw direction of the main body  400  may be indirectly obtained by using two sensors, that is, the yaw-direction encoder  15   b  and the yaw-direction gyro sensor  15   c , installed on the RCWS  100 . In other words, an angular speed in the yaw direction of the main body  400  may be obtained by subtracting a rotational angular speed of the RCWS  100 , that is, a differential value of a yaw-direction encoder angular signal, from a yaw-direction gyro angular speed of the RCWS  100  rotatably mounted on the main body  400 . This may be simply expressed as follows:
 
 W   z,h   =W   z,gyro   −W   z,enc   [Equation 1]
 
     In Equation 1 above, “W z,h ” denotes a yaw-direction disturbance angular speed of a vehicle, “W z,gyro ” denotes a yaw-direction gyro angular speed mounted on the main body  400  of the RCWS  100 , and “W z,enc ” denotes a rotational angular speed of the RCWS  100  itself, that is, a differential value of an encoder angular signal of the yaw-direction encoder  15   b.    
       FIG. 2  is a perspective view illustrating an example of the RCWS  100  of  FIG. 1A . The RCWS  100  may include a weapon unit  200  and an imaging unit  110 . The imaging unit  110  captures an image including a target (not shown). The weapon unit  200  shoots on the target. 
     The imaging unit  110  is coupled to the weapon unit  200  via an imaging unit driving unit  120 . The imaging unit  110  captures an input image and may measure a target distance corresponding to a distance from the weapon unit  200  to the target. The imaging unit driving unit  120  may rotate the imaging unit  110  around at least one axis. 
     The imaging unit  110  may include a day-time camera (not shown), a night-time camera (not shown), and a rangefinder (not shown). The day-time camera may capture a day-time image and the night-time camera may capture a night-time image. The rangefinder may measure a target distance. 
     The imaging unit driving unit  120  may include an imaging unit driving motor  121 , an encoder  122 , and a decelerator  123 . The imaging unit driving motor  121  provides a driving force to rotate the image unit  110  in at least one direction. The encoder  122  detects an amount of rotation of the imaging unit  110 . The decelerator  123  decelerates rotation of the imaging unit driving motor  121 . 
     The weapon unit  200  may include a shooting unit  210  that shoots on the target. The shooting unit  210  may be a gun or artillery capable of firing toward the target. 
     The driving unit  30  of the weapon unit  200  may rotate the shooting unit  210  around a first axis X t . The weapon unit  200  may include the driving unit  30  for generating a rotational driving force, the transfer unit  40  for transferring the rotational driving force of the driving unit  30  to the rotating shaft  20  of  FIG. 1A , and the second sensing unit  25  for sensing the rotational speed ω L  of the rotating shaft  20 . 
     The driving unit  30  generates a driving force to rotate the shooting unit  210  around at least the first axis X t . The second sensing unit  25  senses a rotational speed of the shooting unit  210 . The transfer unit  40  decelerates rotation of the driving unit  30 . 
     The shooting unit  210  of the weapon unit  200  is rotatably installed on the main body  400  via the rotating shaft  20  of  FIG. 1A . Also, the weapon unit  200  may be coupled to the main body  400  to be capable of rotating around a second axis X p  in a vertical direction via a horizontal rotation driving unit  410 . 
     According to the RCWS  100  configured as above, the shooting unit  210  may sense the target and perform shooting while performing a tilting motion (elevation motion) by rotating around the first axis X t  and a panning motion (yaw motion?) by rotating around the second axis X p . 
     Referring to  FIG. 1A , the RCWS  100  may include the first sensing unit  15  to sense the rotational speed ω h  of a rotation of the main body  400 . Since the present embodiment is not limited to the above arrangement position of the first sensing unit  15 , the first sensing unit  15  may be embodied by installing a separate sensor on the main body  400 . 
     Shaking of the main body  400  may instantly cause an abrupt change in replacement of the RCWS  100 . The driving unit  30  generates power to make the RCWS  100  aim at the target while the main body  400  travels around a tough terrain such as a mountainous area to perform target sensing and shooting jobs. The power generated by the driving unit  30  can stabilize the RCWS  100 , that is, a load. 
     The rotating shaft control system according to the present embodiment is a system adopting a stabilization control algorithm for stabilizing a control operation of the RCWS  100  based on an analysis formed by a mechanical driving mechanism. Such a rotating shaft control system may improve a target aiming ability. 
     Although following description discusses the stabilization based on an analysis formed by the mechanical driving mechanism around the first axis X t , the rotating shaft control system of the exemplary embodiments is not limited thereto. For example, the rotating shaft control system may be applied to control of a rotational motion of the RCWS  100  around the second axis X p  or control of a rotational motion of the imaging unit  110 . 
       FIG. 3  is a block diagram illustrating constituent elements of the rotating shaft control system applied to the RCWS  100  of  FIG. 1A . Referring to  FIG. 3 , the rotating shaft control system according to the present embodiment includes the rotating shaft  20  rotatably installed on the main body  400 , the driving unit  30  for driving the rotating shaft  20 , the first sensing unit  15  for sensing the angular acceleration α h  of a rotation of the main body  400 , the second sensing unit  25  of  FIG. 1A  for sensing the rotational speed ω L  of the rotating shaft  20 , the transfer unit  40  for connecting the rotating shaft  20  and the driving unit  30  and transferring a driving force, a motion compensation unit  55  for generating a compensation signal to compensate for an influence by the rotational speed ω h  of the main body  400  and a stabilization control unit  51  for controlling the driving unit  30  based on a compensation torque signal T m  and a difference between the rotational speed ω L  of the rotating shaft  20  and an input signal ω r  input to the stabilization control unit  51  for controlling the driving unit  30 . 
     The motion compensation unit  55  and the stabilization control unit  51  form the control unit  50  for controlling driving of a mechanical system  10  formed by the driving unit  30 , the transfer unit  40 , the rotating shaft  20 , and a load  27 . 
     The control unit  50  may be embodied, for example, by a printed circuit board having various electronic parts and circuit patterns, by a semiconductor chip including software or circuits, or by software that is executable in a computer. 
     Also, each of the motion compensation unit  55  and the stabilization control unit  51  may be separately embodied in at least one form of a printed circuit board, a semiconductor chip, a part of circuits on a printed circuit board, and software. 
       FIG. 4  is a perspective view schematically illustrating a structure of mechanical elements of the rotating shaft control system of  FIG. 3 .  FIG. 5  is a view schematically illustrating a mechanical relationship among mechanical elements of  FIG. 4 . 
       FIG. 4  schematically illustrates a coupling relationship of mechanical elements of the mechanical system  10  controlled by the control unit  50  in the rotating shaft control system of  FIG. 3 . In  FIGS. 3 and 4 , the load  27  denotes elements such as the shooting unit  210  rotated by the rotating shaft  20 . 
     Referring to  FIG. 5 , it may be interpreted how the rotational speed ω h  of a vehicle, that is, the main body  400  affects the mechanical system  10  in stabilizing the load  27 . In  FIG. 5 , tangential speeds at points A and B may be expressed by Equation 2 and 3 and a gear ratio of the overall mechanical system  10  may be expressed by Equation 4. 
     Referring to  FIGS. 4 and 5 , the transfer unit  40  that connects the driving unit  30  and the rotating shaft  20  of the load  20  comprises a first gear assembly  41  and a second gear assembly  42 . Each of the first gear assembly  41  and the second gear assembly  42  comprises a plurality of gears  41   a ,  41   b ,  42   a , and  42   b  that are connected to each other and rotate together.
 
{right arrow over (ν A )}=( r   4   +r   3 )ω h   +r   3 ω 2   =r   4 ω L   [Equation 2]
 
{right arrow over (ν B )}=( r   4   +r   3   +r   2   +r   1 )ω h   −r   1 ω 1 =( r   4   +r   3 )ω h   −r   2 ω 2   [Equation 3]
 
     
       
         
           
             
               
                 
                   N 
                   = 
                   
                     
                       
                         r 
                         2 
                       
                       
                         r 
                         1 
                       
                     
                     ⁢ 
                     
                       
                         r 
                         4 
                       
                       
                         r 
                         3 
                       
                     
                   
                 
               
               
                 
                   [ 
                   
                     Equation 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     4 
                   
                   ] 
                 
               
             
           
         
       
     
     Equation 5 may be obtained by summarizing Equation 3 with respect to ω 2 . 
     
       
         
           
             
               
                 
                   
                     
                       r 
                       2 
                     
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                       2 
                     
                   
                   = 
                   
                     
                       
                         
                           
                             r 
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                             r 
                             4 
                           
                         
                         
                           r 
                           3 
                         
                       
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                   [ 
                   
                     Equation 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     5 
                   
                   ] 
                 
               
             
           
         
       
     
     A rotational speed ω 1  of the driving unit  30  may be obtained by developing Equation 6. 
     
       
         
           
             
               
                 
                   
                     
                       
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                     ⁢ 
                     
                         
                     
                     ⁢ 
                     6 
                   
                   ] 
                 
               
             
             
               
                 
                   
                     
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                       1 
                     
                   
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                                 2 
                               
                               ⁢ 
                               
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                                 4 
                               
                             
                             
                               
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                                 r 
                                 3 
                               
                             
                           
                         
                         ⁢ 
                         
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                           L 
                         
                       
                       + 
                       
                         
                           
                             
                               r 
                               2 
                             
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                               4 
                             
                           
                           
                             
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                     ∴ 
                     
                         
                     
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                       1 
                     
                   
                   = 
                   
                     
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                       ⁢ 
                       
                           
                       
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                         L 
                       
                     
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                         h 
                       
                     
                   
                 
               
               
                 
                     
                 
               
             
           
         
       
     
       FIG. 6  is a conceptual view schematically illustrating a relationship of mechanical elements of  FIG. 5  by using a physical model. Considering movement of the main body  400 , a physical model of mechanical elements forming a mechanical system may be expressed by a two-mass system as illustrated in  FIG. 6 . 
     Referring to  FIGS. 3 and 6 , assuming that a rotational inertia mass of the driving unit  30  is J m , a rotational inertia mass of the load  27  is J o , an overall gear ratio of the transfer unit  40  is N, a compensation torque signal of the driving unit  30  is T m , a torque of disturbance is T d  (corresponding to a moment due to friction or imbalance), an overall torsional deformation spring constant of mechanical elements connecting the load  27  to the driving unit  30  is k eq,m , the rotational angle of the driving unit  30  is θ m , a rotational angle of the load  27  is θ L , and a torsional rotational angle due to an error in consideration of overall angle due to the torsional deformation of the mechanical elements between the driving unit  30  and the load  27  is θ 1 , a motion equation such as Equations 7 and 8 may be established.
 
 J   m {umlaut over (θ)} m   +k   eq,m (θ m −θ 1 )= T   m   [Equation 8]
 
 J   o {umlaut over (θ)} L   +Nk   eq,m (θ 1 −θ m )= T   d   [Equation 8]
 
     Also, Equation 9 may be obtained by integrating Equation 4 with respect to angular speeds to obtain an equation with respect to angles.
 
θ 1   =Nθ   L −( N− 1)θ h   [Equation 9]
 
     Equations 10 and 11 are obtained by substituting Equation 9 into Equations 7 and 8 and summarizing the same.
 
 J   m {umlaut over (θ)} m   +K   eq,m θ m   −NK   eq,m θ L   =−K   eq,m ( N− 1)θ h   +T   m   [Equation 10]
 
 J   o {umlaut over (θ)} L   +N   2   K   eq,m θ L   −NK   eq,m θ m   =K   eq,m   N ( N− 1)θ h   +T   d   [Equation 11]
 
     Equations 12 and 13 are obtained by differentiating Equations 10 and 11 and summarizing the same. 
     
       
         
           
             
               
                 
                   
                     
                       
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                         m 
                       
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                         L 
                       
                     
                   
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                     ⁢ 
                     
                         
                     
                     ⁢ 
                     12 
                   
                   ] 
                 
               
             
             
               
                 
                   
                     
                       
                         J 
                         o 
                       
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                   = 
                   
                     
                       
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                       ⁢ 
                       
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                         ⁡ 
                         
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                         d 
                       
                     
                   
                 
               
               
                 
                   [ 
                   
                     Equation 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     13 
                   
                   ] 
                 
               
             
           
         
       
     
       FIG. 7  is a block diagram illustrating a physical model of  FIG. 6 . The two-mass system of  FIG. 6 , which may be expressed by Equations 12 and 13, may be also expressed by the block diagram of  FIG. 7 . 
     As it may be seen from Equations 12 and 13 and the block diagram of  FIG. 7 , the RCWS  100  corresponding to the two-mass system may be stabilized through feedback control in which the angular speed (=that is, the rotational speed) ω L  of the rotating shaft  20  is fed back as an input of the control system. However, the rotational speed ω h  of the main body  400  has a negative impact on the physical model of the RCWS  100 . In other words, an error flows into the input of the control system as an input signal when the rotational speed ω L  of the rotating shaft  20  is fed back and thus stabilization performance of the RCWS  100  may be deteriorated. 
     In order to stabilize the RCWS  100 , the rotational angle θ L  of the load  27  is made to be 0. When a transfer function using the rotational angle θ L  of the load  27  as an output value and the compensation torque signal T m  of the driving unit  30  as an input value is obtained from Equations 10 and 11, the transfer function may be expressed by Equations 14 and 15. 
     
       
         
           
             
               
                 
                   
                     θ 
                     L 
                   
                   = 
                   
                     
                       
                         
                           
                             ( 
                             
                               N 
                               - 
                               1 
                             
                             ) 
                           
                           ⁢ 
                           
                             NK 
                             
                               eq 
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                               m 
                             
                           
                         
                         
                           p 
                           ⁡ 
                           
                             ( 
                             s 
                             ) 
                           
                         
                       
                       ⁢ 
                       
                         J 
                         m 
                       
                     
                     ⁢ 
                     
                       ∝ 
                       h 
                     
                     ⁢ 
                     
                       
                         
                           + 
                           
                             
                               NK 
                               
                                 eq 
                                 , 
                                 m 
                               
                             
                             
                               p 
                               ⁡ 
                               
                                 ( 
                                 s 
                                 ) 
                               
                             
                           
                         
                         ⁢ 
                         
                           T 
                           m 
                         
                       
                       + 
                       
                         
                           
                             { 
                             
                               
                                 
                                   J 
                                   m 
                                 
                                 ⁢ 
                                 
                                   s 
                                   2 
                                 
                               
                               + 
                               
                                 K 
                                 
                                   eq 
                                   , 
                                   m 
                                 
                               
                             
                             } 
                           
                           
                             p 
                             ⁡ 
                             
                               ( 
                               s 
                               ) 
                             
                           
                         
                         ⁢ 
                         
                           T 
                           d 
                         
                       
                     
                   
                 
               
               
                 
                   [ 
                   
                     Equation 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     14 
                   
                   ] 
                 
               
             
             
               
                 
                   
                       
                   
                   ⁢ 
                   
                     
                       
                         p 
                         ⁡ 
                         
                           ( 
                           s 
                           ) 
                         
                       
                       = 
                       
                         
                           J 
                           m 
                         
                         ⁢ 
                         
                           J 
                           o 
                         
                         ⁢ 
                         
                           s 
                           4 
                         
                         ⁢ 
                         
                           { 
                           
                             
                               s 
                               2 
                             
                             + 
                             
                               ω 
                               p 
                               2 
                             
                           
                           } 
                         
                       
                     
                     , 
                   
                 
               
               
                 
                   [ 
                   
                     Equation 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     15 
                   
                   ] 
                 
               
             
             
               
                 
                   
                       
                   
                   ⁢ 
                   
                     
                       ω 
                       p 
                       2 
                     
                     = 
                     
                       
                         
                           ( 
                           
                             
                               J 
                               o 
                             
                             + 
                             
                               
                                 N 
                                 2 
                               
                               ⁢ 
                               
                                 J 
                                 m 
                               
                             
                           
                           ) 
                         
                         ⁢ 
                         
                           K 
                           
                             eq 
                             , 
                             m 
                           
                         
                       
                       
                         
                           J 
                           m 
                         
                         ⁢ 
                         
                           J 
                           o 
                         
                       
                     
                   
                 
               
               
                 
                     
                 
               
             
           
         
       
     
     In Equation 14, “α h ” denotes an angular acceleration obtained by differentiating the rotational speed ω h  of the main body  400 . When a value of the compensation torque signal T m  to remove an angular acceleration component is obtained from Equation 14, the value may be expressed by Equation 16.
 
 T   m =−( N− 1) J   m α h   [Equation 16]
 
     Equation 16 may be independently used for each of the yaw direction and the elevation direction. The compensation torque signal T m  for motor torque corresponding to each direction is all independently calculated and used. Thus, a motor for driving the RCWS  100  in the yaw direction and a motor for driving the RCWS  100  in the elevation direction each may be independently driven and controlled. 
     All equations for compensating for a disturbance angular speed of the main body  400  may be identically applied to both of the yaw direction and the elevation direction. 
     When Equation 16 is substituted into Equation 14, a transfer function using the rotational angle θ L  of the load  27  as an output value and having the disturbance torque T d  may be expressed by Equation 17. 
     
       
         
           
             
               
                 
                   
                     θ 
                     L 
                   
                   = 
                   
                     
                       
                         { 
                         
                           
                             
                               J 
                               m 
                             
                             ⁢ 
                             
                               s 
                               2 
                             
                           
                           + 
                           
                             K 
                             
                               eq 
                               , 
                               m 
                             
                           
                         
                         } 
                       
                       
                         p 
                         ⁡ 
                         
                           ( 
                           s 
                           ) 
                         
                       
                     
                     ⁢ 
                     
                       T 
                       d 
                     
                   
                 
               
               
                 
                   [ 
                   
                     Equation 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     17 
                   
                   ] 
                 
               
             
           
         
       
     
     Equation 17 signifies that the rotational angle θ L  of the load  27  for controlling stabilization may become 0 by designing the control system for controlling the RCWS  100  in order to set the compensation torque signal T m  of the driving unit  30  to remove an error due to movement of the main body  400 , and simultaneously to reduce an influence of the disturbance torque T d  in the control system for controlling the RCWS  100 . 
     To reduce an influence of the disturbance torque T d , an imbalanced moment of the load  27  and friction needs to be reduced during the design of the control system for controlling the RCWS  100 . Further, the stabilization control unit  51  of  FIG. 3  may be designed to remove an influence of the disturbance torque T d . 
       FIG. 8  is a block diagram illustrating the stabilization control unit  51  of the rotating shaft control system of  FIG. 1A . Referring to  FIG. 8 , the stabilization control unit  51  included in the rotating shaft control system of  FIG. 1A  may be embodied in a variety of types and  FIG. 8  illustrates an example of various embodiments thereof. The stabilization control unit  51  may include an integral controller  52  for integrating a difference e=(ω r −ω L ) between the rotational speed ω L , that is, a speed of the load  27 , and the stabilization input signal ω r  and a proportional-derivative controller  53  using the rotational speed ω L  of the rotating shaft  20  as an input. The stabilization control unit  51  may output a control signal Tc by adding the compensation torque signal T m  and an output signal of the integral controller  52  and subtracting an output signal of the proportional-derivative controller  53  therefrom. 
     The embodiment of the rotating shaft control system of  FIG. 1A  is not limited to the detailed structure of the stabilization control unit  51  of  FIG. 8  and may be modified to other types. For example, the stabilization control unit  51  may include at least one of a proportional controller, an integral controller, and a derivative controller. 
       FIG. 9  is a graph showing a degree of accuracy with respect to stabilization when a pitch motion having a size of 1 Hz is applied to the main body  400  in the rotating shaft control system of  FIG. 3 .  FIG. 10  is a graph showing a degree of accuracy with respect to stabilization when a pitch motion having a size of 2 Hz is applied to the main body  400  in the rotating shaft control system of  FIG. 3 . 
     In  FIGS. 9 and 10 , a line “w/VMC” indicates a result when the motion compensation unit  55  of  FIG. 3  is operated to perform a motion compensation function, and a line “w/o VMC” indicates an influence of a motion of the main body  400  on a degree of accuracy with respect to stabilization when the motion compensation unit  55  is not operated. A pitch motion is applied to the main body  400  by using a simulator with 6 degrees of freedom. 
     Table 1 indicates results of measurement of a stabilization precision degree indicated in  FIGS. 9 and 10 . It can be seen that a stabilization precision degree is improved when the rotating shaft control system according to the present embodiment is in use by 42% with respect to the maximum when the rotating shaft control system is not used. 
     
       
         
               
               
             
               
               
               
               
             
               
               
               
               
               
             
           
               
                   
                 TABLE 1 
               
             
             
               
                   
                   
               
               
                   
                 Stabilization Precision Degree (mrad RMS) 
               
             
          
           
               
                   
                 Vehicle motion 
                 Vehicle motion 
                   
               
               
                 Disturbance 
                 compensation 
                 compensation 
               
               
                 Frequency 
                 not applied 
                 applied 
                 Remarks 
               
               
                   
               
             
          
           
               
                 Vehicle 
                 1.0 
                 0.73 
                 0.42 (Decreased by 0.31) 
                 Improved 
               
               
                 Pitch 
                 Hz 
                   
                   
                 by 42% 
               
               
                 Motion 
                 2.0 
                 0.72 
                 0.53 (Decreased by 0.19) 
                 Improved 
               
               
                 Disturbance 
                 Hz 
                   
                   
                 by 26% 
               
               
                   
               
             
          
         
       
     
     As described above, according to the rotating shaft control system according to the above-described embodiments, an error component generated when a rotational motion of a main body is transferred to a mechanical system may be effectively removed by the operation of the motion compensation unit and the stabilization control unit so that a degree of accuracy with respect to stability is improved. 
     While this invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims. The exemplary embodiments should be considered in a descriptive sense only and not for purposes of limitation.