Abstract:
A three dimensional wire flying system includes a plurality of winches collectively hanging an object and a control unit for controlling the plurality of winches and the main safety device. Each of the plurality of winches includes a drum unit, a wire wound on the drum unit, a motor unit which provides power to the drum unit, a brake module which stops rotation of the drum unit, a limit switch which operates upon detecting a hardware limit state, and a servo-system. Each of the plurality of winches operates to move the object in a three dimensional space in three directions, including an up-down direction, a left-right direction and a forward-backward direction, and each winch provides a multi-level safety protection.

Description:
CROSS-REFERENCES TO RELATED APPLICATION 
     This patent application is a U.S. national phase under 35 U.S.C 371 of PCT/KR2012/000720 filed on Jan. 31, 2012, which claims the benefit of priority from Korean Patent Application No. 10-2011-0028117, filed on Mar. 29, 2011, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference in its entirety. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a three dimensional (3D) wire flying system. 
     2. Description of the Related Art 
     Fail-safe is generally known to be a device to prevent or minimize harm in advance by employing a multilevel of safety measures, when the harm is likely due to fault in a system or manmade fault. 
     For example, when power supply to an elevator is ceased, thereby bringing the elevator to a sudden stop in operation, an emergency brake is operated to keep elevator from falling so as to secure the passengers&#39; lives until rescue gets to the site. Additional examples may include multi-protective device of nuclear reactor, a mixer device which does not operate blades unless cap is securely sealed, a circuit breaker trip which prevents electric fire, a fail-safe system (derailing point, safety siding, on-board receiver, way-side transmitter, driver alarm system, emergency brake, etc.) implemented in rail facility. 
     The fail-safe may also be implemented in a system utilizing winch. For example, a wire flying system which employs a combination of a plurality of winches involves unexpected damages when abnormality occurs in the winches or software that controls the winches, or when abnormality occurs in a hardware that detects and manages abnormality of the winches or the controlling software. 
     Accordingly, in order to prevent or minimize possible harm that can occur due to various causes particularly in a system that utilizes winches, demand is increasing for a winch fail-safe that can ensure safe use of the winches in various levels. 
     SUMMARY OF THE INVENTION 
     Technical Problems 
     Accordingly, the present invention has been created to solve the problems mentioned above, and it is an object of the present invention to provide a three dimensional (3D) wire flying system which is capable of preventing at various levels a possible harm that can occur in a system utilizing winches due to various causes. 
     Means to Solve the Problems 
     In order to achieve the objects explained above, the present invention provides a three dimensional wire flying system which hangs an object on a wire adjustable in its length by a winch and moves the object in a three dimensional space, wherein the winch includes a drum unit on or from which the wire is wound or unwound, a motor unit which provides power to the drum unit, a brake module which stops rotation of the drum unit, a limit switch which operates upon detecting a hardware limit state, and a servo-system which controls the motor unit in response to a command from a control unit, determines state of the wire and the motor unit according to a local safety logic and transmits the state of the wire and the motor unit to the control unit. The three dimensional space includes a first range, a second range corresponding to a preset safe length of the wire, and a third range corresponding to a preset permissible length range of the wire. If the local safety logic determines that operating range of the wire deviates from the first range only, the local safety device transmits information about the deviation from the first range to the control unit, and the control unit transmits a software limit signal to the servo-system to control the motor unit, so that the operating range of the wire returns into the first range. If the local safety logic determines that the length of the wire deviates from the second range, the local safety device transmits information about the deviation from the second range to the control unit, and the control unit transmits a software limit signal to the servo-system to stop the operation of the motor unit. If the local safety logic determines that the length of the wire deviates from the third range, the limit switch detects hardware limit state and mechanically stops the operation of the motor unit to thus stop the rotation of the drum unit, thereby implementing safety control at hardware level. 
     If the local safety logic may determine a local warning state in which the power provided by the motor unit to the drum unit is 0 or deviates from a preset power range, the local safety device transmits information about the local warning state to the control unit, and the control unit may stop the operation of the motor unit. 
     The second range may be included in the third range. 
     The winch may include one or more winches, and the three dimensional wire flying system may include an integrated safety device which determines state of the one or more winches according to a safety logic and transmits information about the state of the one or more winches to the control unit. 
     If the safety logic determines a warning state in which any of the one or more winches has deviation of the length of the wire unwound from the drum unit from the second range or in which the power provided by the motor unit to the drum unit deviates from a preset power range, the integrated safety device may transmit information about the warning state to the control unit and the control unit may stop the operation of the one or more winches altogether. 
     If any of the one or more winches is determined to be in local warning state via the local safety device, the local safety device may transmit information about the local warning state to the integrated safety device to implement an integrated synchronous motion in which the integrated safety device stops the operation of the one or more winches altogether. 
     The integrated safety device may transmit information about the warning state to the local safety devices of the one or more winches to implement a local synchronous motion in which the local safety devices of the one or more winches stop the operation of the one or more winches, respectively. 
     The three dimensional wire flying system may additionally include an emergency switch which, independently from the local safety device or the integrated safety device, mechanically detects emergency state to control the motor unit and the brake module. 
     Effect of the Invention 
     According to the present invention, safety control is ensured based on dual-system of a local safety device and an integrated safety device, in which stopping of the winch at software level and hardware level are implemented in stepwise manner, and efficient stop is implemented based on mechanical detection at an emergency switch, whereby possible harm that may arise in a three dimensional (3D) flying system due to various causes can be prevented at several levels. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and/or other aspects and advantages of the present invention will become apparent and more readily appreciated from the following detailed description, taken in conjunction with the accompanying drawings of which: 
         FIG. 1  is a schematic perspective view of a winch according to one embodiment of the present invention; 
         FIG. 2  is a schematic, exploded perspective view of the winch of  FIG. 1 ; 
         FIG. 3  is a schematic view of a winch safety system utilizing a winch according to one embodiment of the present invention; 
         FIG. 4  is a conceptual view provided to explain a three dimensional wire flying system utilizing a winch according to one embodiment of the present invention; and 
         FIG. 5  is a flowchart provided to explain stepwise operation of a three dimensional wire flying system according to one embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Certain embodiments of the present invention will be explained below with reference to the accompanying drawings. 
       FIG. 1  is a schematic perspective view of a winch according to one embodiment of the present invention, and  FIG. 2  is a schematic, exploded perspective view of the winch of  FIG. 1 . 
     Referring to  FIGS. 1 and 2 , a winch  100  according to one embodiment of the present invention includes a drum unit  1 , a motor unit  2 , a brake module  3 , a limit switch  6 , and a servo-system  4 . The winch  100  may additionally include a manually-driven control unit or a manual control unit  5  and an emergency switch. 
     First, the constitution of the drum unit  1  is explained below. The drum unit  1  is rotatably formed such that a wire  11  is wound or unwound thereon. By way of example, referring to  FIG. 1 , the drum unit  1  may include a drum in a cylindrical shape lying in a horizontal direction, along the circumference of which the wire  11  is either wound or unwound, and a rotating shaft connected to the motor unit  2  (to be explained below) to rotate the drum. 
     Next, the constitution of the motor unit  2  is explained. 
     The winch  100  is used in a manner in which the wire is wound around the drum unit  1  and unwound to a necessary length for use and then rewound, and the motor unit  2  supplies power to the drum unit  1  to wind or unwind the wire  11 . The power supplied from the motor unit  2  may be implemented in the form of an output torque of a motor  21 , although certain variations are possible. Further, the motor unit  2  may be connected to one end of the rotating shaft of the drum unit  1  to rotate the drum, thereby winding or unwinding the wire  11 . The motor unit  2  may be arranged on one side of the drum unit  1  as illustrated in  FIGS. 1 and 2 . 
     Referring to  FIGS. 1 and 2 , the motor unit  2  may include a motor  21  which provides power, and a pulley  22  which transmits the power of the motor  21  to the drum unit  1 . For reference, the motor  21  may include an electronic brake provided therein. In response to a command to stop received at a software level via the control unit  400 , the motor  21  may be stopped by the electronic brake. Further, the electronic brake inside the motor  21  may operate in association with a limit switch  6  or emergency switch, when a command to stop is received at a hardware level via the limit switch  6  or emergency switch. The motor unit  2  may include a coupling  23  which engages the rotating shaft of the motor  21  provided as the power generator to the rotating shaft of a moving device including the pulley  22 , thereby allowing the power from the motor  21  to be transmitted. 
     Next, the constitution of the brake module  3  will be explained. 
     The brake module  3  plays a role of stopping the rotation of the drum unit  1 . Referring to  FIGS. 1 and 2 , the brake module  3  may be arranged on the other side of the drum unit  1 . For example, the brake module  3  may be connected to the other end of the rotating shaft of the drum unit  1  to stop the rotation of the drum. Further, the brake module  3  may be an electronic brake type. 
     By way of example, if operation of the motor  21  is stopped via the limit switch  6  or emergency switch, which will be explained below, the brake module  3  is operated to rapidly stop the rotation of the drum unit  1 . For reference, the electronic brake inside the motor  21  may also operate to ensure faster stopping of the rotation of the drum  1 . 
     Next, the constitution of the limit switch  6  will be explained. 
     The limit switch  6  operates upon detecting a hardware limit state. By way of example, the hardware limit state may include a situation in which the length of the wire unwound from the drum unit  1  exceeds a preset permissible length range. Upon detecting the hardware limit state, the limit switch  6  mechanically blocks power to the motor unit  2  and operates the brake module  3  to thus stop the rotation of the drum unit  1 . The brake module  3  may stop the rotation of the drum unit  1  via the electronic brake, and the electronic brake inside the motor  21  may also operate to ensure faster stopping of the rotation of the drum unit  1 . For reference, the limit switch  6  may be provided in the motor unit  2 , as exemplarily shown in  FIG. 2  in dotted lines. 
     That is, the limit switch  6  may be implemented at a hardware level to mechanically block the power supply to the motor  21  to stop the operation thereof. By employing the limit switch  6  with the mechanical stopping mechanism in the winch  100 , it is possible to ensure rapid stopping of the operation of the motor  21 , particularly when it is necessary to stop the motor  21  faster than by stopping it through the route of using software level of stop command from the control unit  400 . The example of operating the limit switch  6  will be explained in greater detail below with reference to the constitution of a local safety device  42 . 
     For reference, the control unit  400  will be explained with reference to a winch safety system  1000  according to one embodiment of the present invention. 
     Next, the constitution of the servo-system  4  will be explained. 
     The servo-system  4  controls the motor unit  2  in accordance with a command from the control unit  400 . Referring to  FIGS. 1 and 2 , the servo-system  4  may be arranged on one side of the motor unit  2 . Further, the servo-system  4  may be connected to the motor unit  2  by wired or wireless manner to control the motor unit  2 . For reference, the servo-system  4  may utilize a motor brake of the motor  21  to stop the driving of the motor unit  2  at a software level. 
       FIG. 3  is a schematic view of a winch safety system utilizing a winch according to one embodiment of the present invention. 
     Referring to  FIG. 3 , the servo-system  4  provided in the winch  100  may include the local safety device  42  and may additionally include a servo-driver unit  41 . 
     The servo-driver unit  41  may refer to a portion of the servo-system  4  that controls the motor unit  2  according to the command from the control unit  400 . For example, the servo-driver unit  41  may include a subordinate communication unit which exchanges information with external devices such as the control unit  400  by EtherCAT. 
     Further, the local safety device  42  may determine the state of the winch  100 , for example, the state of the wire  11  and the motor unit  2  according to local safety logic. The local safety device  42  may transmit the result of determining the state of the winch  100  according to the local safety logic to the control unit  400 . As explained below, the information about the state of the winch  100  may include information about length of the wire  11  or output torque (power) of the motor unit  2 , which may be transmitted to the control unit  400  as specific information or simple signal concept depending on needs. 
     As used herein, the ‘local safety logic’ may involve a procedure of logic to monitor the winch  100  and determine the state via the local safety device  42 , but not limited thereto. That is, various methods may be implemented for the local safety logic to determine the safe state. 
       FIG. 4  is a conceptual view provided to explain a three dimensional wire flying system utilizing a winch according to one embodiment of the present invention. 
     For example, referring to the first range illustrated in  FIG. 4 , if determining via the local safety logic that the current state is that the operating range of the wire  11  deviates from the first range only, the local safety device  42  transmits information about the deviation from the first range to the control unit  400  and the control unit  400  transmits a software limit signal to the servo-system  4  (e.g., servo-driver unit  41 ) to control the motor unit  2  so that the operating range of the wire  11  returns within the first range. That is, in the situation where the level of emergency is not too high to abruptly stop the winch  100 , the control unit  400  may safely control the wire  11  via the command at software level. 
     Next, referring to the second range illustrated in  FIG. 4 , if determining via the local safety logic that the current wire state is the local warning state in which the length of the wire  11  unwound from the drum unit  1  exceeds a preset safe length (i.e., deviation from the second range), the local safety device  42  transmits information about the local warning state to the control unit  400 , and the control unit  400  may transmit a software limit signal to the servo-system  4  (e.g., servo-driver unit  41 ) to stop the operation of the motor unit  2 . For example, according to the control unit  400 , the operation of the motor unit  2  may be stopped by the braking of the motor unit  2  itself. 
     The preset safe length (e.g., second range of  FIG. 4 ) may be included in a preset permissible length (e.g., third range of  FIG. 4 ) which will be explained in detail below. If the length of the currently-used wire  11  exceeds the preset permissible range (i.e., deviates from the third range), the limit switch  6  may mechanically perceive the hardware limit state as explained above and therefore, safe control at hardware level may be performed. 
     As explained above, the local safety logic may be so configured that the safe control at software level based on a preset range of safe length precedes the other controls, in which case the preset safe control at hardware level may be performed based on the preset permissible length when there is an abnormality in the safe control at software level. 
     Further, with respect to an aspect of the power provided to the drum unit  1 , if the local safety logic determines the current state of the motor unit  2  to be the local warning state in which the power provided from the motor unit  2  to the drum unit  1  exceeds a preset power range, likewise in the local warning state where the length of the wire  11  unwound from the drum unit  1  exceeds the preset safe length, the local safety device  42  may transmit the information of the local warning state to the control unit  400  and the control unit  400  may stop the operation of the motor unit  2 . 
     Based on a concept of output torque, the ‘preset power range’ as used herein may refer to the output torque of the motor  21  greater than 0 and less than a maximum permissible torque. If the output torque of the motor  21  is 0 or outside the maximum permissible torque during operation of the motor unit  2 , such may indicate the presence of an abnormality in the motor  21 . 
     Referring to the third range illustrated in  FIG. 4 , in a hardware limit state (i.e., deviation from third range) in which the length of the wire  11  unwound from the drum unit  1  for use exceeds a preset permissible length range, the limit switch  6 , which mechanically detects the hardware limit state and operates accordingly, may mechanically block the power supply to the motor unit  2  and operate the brake module  3  to stop the rotation of the drum unit  1 . At this time, the electronic brake provided in the motor  21  may also operate. 
     That is, if the length of the wire  11  in use exceeds the preset permissible length range, which is further aggravated situation than when the length deviates from the preset safe length, the safe control may be implemented so that instead of stopping the operation of the motor unit  2  via limit signal at software level, the limit switch  6  may operate based on the limit detection performed at hardware level. 
     The ‘preset permissible length range (e.g., third range illustrated in  FIG. 4 ) as used herein may be the widest range that is set, outside of which there is a potential problem of the safety. In other words, the ‘preset permissible length range’ may be a range of wire length that is so set as to mechanically operate the limit switch  6  independently from the other safety systems and thus ensure safety, when the safety system does not operate normally via software level command due to abnormality that may occur for software fault (S/W fault) in the multi safety system. 
     Further, the ‘preset length range’ as used herein may refer to a range of length of the wire  11  unwound from the drum unit  1  to be used, i.e., refer to the range that is preset to form a safe area for wire flying in the construction of a wire flying system. 
     Furthermore, in an emergency such as power failure, or glitch in safety logic, control unit  400 , limit switch  6  or motor unit  2 , the emergency switch may mechanically block the power supply to the motor unit  2  and stop the rotation of the drum unit  1  by operating the brake module  3 . At this time, the electronic brake provided in the motor  21  may also operate. The emergency switch will be explained below with reference to the winch safety system  1000  according to one embodiment of the present invention. 
     Next, the constitution of the manual control unit  5  will be explained. 
     The manual control unit  5  may manually control the motor unit  2  and the brake module  3 . By way of example, referring to  FIGS. 1 and 2 , the manual control unit  5  may be provided in front of the motor unit  2 , and in the form of a switch panel. In additional to the automatic safety system including the local safety device  42  which provides several stages of safety as explained above, the manual control unit  5  is further provided. Accordingly, dual safety system consisting of automatic and manual safety systems can be provided. Therefore, the winch  100  can be used more safely. 
     Next, the operation of the winch  100  will be explained below with reference to the constitutions explained above. The winch  100  is operated in a manner in which, in normal operation, the motor unit  2  is controlled via the server-driver unit  41  which receives commands from the control unit  400 , so that the wire  11  is wound or unwound to or from the drum unit  1 . By way of example, if the operating range of the wire  11  exceeds the first range only ( FIG. 4 ), the operating range of the wire  11  may be controlled at software level via the control unit  42  so that the operating range is returned to within the first range. 
     Then if the operating range of the wire  11  deviates from the second range (i.e., preset safe length range) illustrated in  FIG. 4 , the safe control may be implemented in which the driving of the motor unit  2  of the winch  100  is stopped at a software level via a stop command received from the control unit  42 . The motor unit  2  may be stopped by the motor braking of the motor unit  2  itself, or the electronic brake of the motor  21  may operate. 
     Furthermore, if the operating range of the wire  11  deviates from the third range (i.e., preset permissible length range), this may be an abnormal situation where there is a problem in the safe control at software level via the control unit  42 . That is, in a hardware limit state, which is very urgent, the limit switch  6 , which operates independently from the local safety device  42  based on mechanical detection, may rapidly stop the driving of the winch  100 . 
     The winch safety system  1000  utilizing the winch  100  explained above according to one embodiment of the present invention will be explained below, in which the elements identical or similar to those explained above with reference to the winch  100  will not be explained or briefly explained for the sake of brevity. 
     Referring to  FIG. 3 , the winch safety system  1000  according to one embodiment includes one or more winches  100 , and an integrated safety device  200 . Further, the winch safety system  1000  may additionally include an emergency switch (not illustrated), and a control unit  400 . 
     First, the constitution of the winch  100  will be referenced to the description provided above. 
     Next, the constitution of the integrated safety device  200  will be explained. 
     The integrated safety device  200  may determine the state of one or more winches  100  according to safety logic. Further, the integrated safety device  200  may transmit to the control unit  400  the information regarding the state of one of more winches  100  as determined according to the safety logic. 
     By way of example, referring to  FIG. 3 , the winch safety system  1000  according to one embodiment of the present invention may include four winches  100  each including a servo system  4  consisting of a servo-driver unit  41  and a local safety device  42 , and the integrated safety device  200  may be connected to the servo-systems  4  (e.g., servo-driver units  41 ) to determine the states of the four winches  100  according to the safety logic. 
     The ‘safety logic’ as used herein may refer to a processing of logic to monitor one or more winches  100  via, for example, integrated safety device  200 , and determine the states thereof. That is, various methods for determining safety state may be implemented as the safety logic. 
     For example, referring to the first range illustrated in  FIG. 4 , if the safety logic determines that the operating range of the wire  11  corresponding to any of the one or more winches  100  deviates from the first range ( FIG. 4 ) only, the integrated safety device  200  may transmit the information about the deviation from the first range to the control unit  400 , and the control unit  400  transmits a software level control command to the servo-systems  4  (e.g., servo-driver units  41 ) of one or more winches  100  appropriately to control the corresponding motor units  2 , so that the operating range of the corresponding wires  11  returns back into the first range. That is, because the situation is not too urgent to stop the operation of one or more winches  100 , the command at software level from the control unit  400  may be used to safely control the wire  11 . 
     Next, referring to the second range illustrated in  FIG. 4 , if determining via the local safety logic that any of one or more winches  100  is in the warning state in which the length of the wire  11  unwound from the drum unit  1  exceeds a preset safe length (i.e., deviation from the second range), the integrated safety device  200  may transmit information about the warning state to the control unit  400 , and the control unit  400  may transmit a software limit signal to the servo-system  4  (e.g., servo-driver unit  41 ) of one or more winches  100  to stop the operation of one or more winches  100 . For example, according to the control unit  400 , the operation of the motor unit  2  of one or more winches  100  may be stopped by the braking of the motor unit  2  itself. 
     Further, with respect to an aspect of the power provided from the motor unit  2  to the drum unit  1 , if the safety logic determines that any of one or more winches  100  is in warning state in which the power provided from the motor unit  2  to the drum unit  1  exceeds a preset power range, the integrated safety device  200  may transmit the information of the warning state to the control unit  400  and the control unit  400  may stop the operation of one or more winches  100 . 
     Meanwhile, the integrated safety device  200  may coexist with the local safety devices  42  provided to each of one or more winches  100  in the winch safety system  1000  to be operated in synchronization with each other. 
     If any of one or more winches  100  determines that it is in local warning state via the local safety logic of the corresponding local safety device  42 , the corresponding local safety device  42  transmits information about the local warning state to the integrated safety device  200 , and the integrated safety device  200  may form an integrated synchronous motion to stop the operation of one or more winches  100  altogether. 
     That is, if the local safety device  42  monitors a problem occurring in one of one or more winches  100  so that the corresponding winch  100  is stopped, the integrated safety device  200  may operate together to thus cause the winch safety system  1000  to stop. In other words, if the local safety device  42  provided for one of the winches  100  monitors a problem in the corresponding winch  100  so that the corresponding winch  100  is stopped, the integrated safety device  200  may be synchronized with the respective local safety devices  42  of the winches  100  to control to stop all the other winches  100  too. 
     Further, if the safety logic of the integrated safety device  200  determines that any of one of more winches  100  is in warning state, the information regarding the warning state may be transmitted to the local safety devices  42  of the winches  100 , respectively, to construct a local synchronous motion to cause the local safety devices  42  of the winches  100  to stop the operation of one or more winches  100 , respectively. That is, the local safety devices  42  provided for the respective winches  100  may also operate when the operation is stopped via the integrated safety device  200 , so that the entire winch safety system  1000  may be stopped. 
     For reference, if one of the winches  100  determines via the local safety logic of the corresponding local safety device  42  that it is in local warning state, the corresponding local safety device  42  may transmit information regarding the local warning state to the rest winches  100  so that the rest winches  100  perform jobs to stop operation thereof. 
     As explained above, more stable safety control is implemented, because the local safety device  42  self-monitors the safety state of the winch  100  that the local safety device  42  belongs to, while the integrated safety device  200  generally monitors the safety state of one or more winches  100 , in a manner in which the two safety devices  42 ,  200  are operated in synchronization with each other. 
     Further, referring to the third range illustrated in  FIG. 4 , if any of one or more winches  100  is in hardware limit state (i.e., deviation from third range) in which the length of the wire  11  unwound from the drum unit  1  exceeds a preset permissible length, as explained above, the limit switch  6 , which mechanically detects the hardware limit state and operates accordingly, may mechanically block power supply to the motor unit  2  and operate the brake module  3  to stop the rotation of the drum unit  1 . At this time, the electronic brake provided in the motor  21  may also operate. That is, because limit switches are provided in the winches, respectively, the limit switches may mechanically detect the hardware limit state of each of the winches  100  to rapidly stop the motor unit  2  as explained above. 
     Furthermore, the servo-driver units  41  of one or more winches  100  and the integrated safety device  200  may include subordinate communication units for EtherCAT communication with each other or with the control unit  400 . By way of example, the subordinate communication units may transmit information about the state of the wire  11 , the drum unit  1 , or the motor unit  2  to the control unit  400  and receive information about a command from the control unit  400 . 
     The constitution of the emergency switch will now be explained below. 
     Independently from the local safe devices  42  or the integrated safety device  200 , the emergency switch may mechanically detect abnormal state and control the motor unit  2  and the brake module  3 . To be specific, the emergency switch may mechanically detect abnormal state, block power supply to the motor unit  2  and operate the brake module  3  to stop the rotation of the drum unit  1 . Further, the emergency switch may operate the electronic brake within the motor  21 . 
     By way of example, if the emergency state is caused due to power failure, the emergency switch may be a power-failure emergency switch which determines power failure. The power-failure emergency switch may determine power failure, and block power supply to the motor  21 , while at the same time, operating the brake module  3 . Further, the emergency state may be caused due to a problem in the safety logic, the control unit  400 , the limit switch  6  or the motor unit  2 . 
     Next, the constitution of the control unit  400  will be explained. 
     The control unit  400  may control one or more winches  100  by transmitting a command to control the motor unit  2  to the servo-system  4  of each of the winches  100 . Further, the control unit  400  may receive information about safety state of one or more winches  100  from the local safety device  42  or the integrated safety device  200  and stop the operation of one or more winches  100  at software level. 
     Referring to  FIG. 3 , the control unit  400  may include a main PC and an embedded PC. By way of example, the main system may be a workstation PC which may be implemented as a TwinCAT and EtherCAT Master Stack. Further, the embedded system may be so configured that a command is transmitted to the servo-driver unit  41  of each of the winches  100  for RT motion control of the winch  100 , and receive information about each constituent from each servo-driver unit  41 . By way of example, the embedded system may implement TwinCAT and EtherCAT Master. By the use of the control unit  400  and the subordinate communication units, the winch safety system  1000  according to the present invention may operate as a network-based dispersion control system with fast synchronization control that is performed within 1 msec. 
     Referring to  FIG. 3 , the winch safety system  1000  according to one embodiment of the present invention may additionally include a mechanical emergency stop (ESTOP) button  310  and a rotary limit switch (SW)  320 . Accordingly, multilevel of safety control that employs both automatic and manual controls is possible, because it is additionally possible to mechanically block power supply to the motor unit  2  with the ESTOP button and stop the rotation of the drum unit  1  with the rotary limit SW. 
     The stepwise operation of the winch safety system  1000  having the constitutions explained above will be explained below. 
       FIG. 5  is a flowchart provided to explain stepwise operation of a three dimensional wire flying system according to one embodiment of the present invention. 
     Referring to  FIG. 5 , at S 11  to S 12 , if the local safety device  42  or the integrated safety device  200  determines that the length of the wire  11  in use does not exceed a predetermined safe length range, and determines at S 12  to S 3 , that the output torque of the motor  21  is other than 0 and within a maximum permissible torque, and also if the emergency switch does not operate, the winch  100  is continuously operated in a normal condition. However, if power failure occurs, the power-failure emergency switch is operated at S 3  to S 5 , so that the power supply to the motor of the corresponding winch  100  is blocked, and the rotation of the drum unit  1  is rapidly stopped via the brake module  3 . 
     At S 11  to S 12 , even when the length of the wire  11  in use is yet within the preset safe length range, if the output torque of the motor  21  is 0 or greater than the maximum permissible torque at S 12  to S 1 , the situation may be determined to be in (local) warning state at software level via the (local) safety logic, in which case the local safety device  42  or the integrated safety device  200  may transmit the information about the (local) warning state or synchronize with each other, and the control unit  400  receives the (local) warning state information to stop (at S 1 ) the operation of the motor unit  2  at software level. 
     Further, at S 11  to S 13 , if the length of the wire  11  in use does exceed the preset safe length range, and if the length is yet within the preset permissible range at S 13  to S 1 , such situation may be determined via the (local) safety logic to be the (local) warning state at software level, in which case the local safety device  42  or the integrated safety device  200  may transmit the information about the (local) warning state or synchronize with each other, and the control unit  400  receives the (local) warning state information to stop (at S 1 ) the operation of the motor unit  2  at software level. 
     Further, at S 13  to S 2 , if the length of the wire  11  in use exceed the preset permissible length range, the situation is determined to be in hardware limit state, in which case the limit switch  6  for mechanically detecting such situation and operating accordingly, may mechanically block the power supply to the motor unit  2  and may stop the rotation of the drum unit  1  via the brake module  3  faster than the safety control at software level. 
     According to the present invention, multilevel safety system can be established stably based on virtual operating space setup and implementation thereof over three stages as explained above. Further, because one or more winches  100  each has the manual control unit  5 , user is able to do safety control using the manual control unit  5 . 
     Meanwhile, a method of winch safety control (referred to as ‘winch safety control method’ hereinafter) according to one embodiment will be explained below with reference to  FIG. 5 , in which the explanation about the like elements explained above with reference to the winch  100  or the winch safety system  1000  will be omitted or given briefly for the sake of brevity. 
     For reference, a winch used in the winch safety control method will be given the same reference numeral  100  as the one explained above, and may include components as explained below. 
     Referring to  FIG. 5 , the winch safety control method includes determining a safe length via safety logic in which it is determined if the length of the wire  11  unwound from the winch  100  for use is within a preset safe length range (at S 11 ), determining motor power via the safety logic in which it is determined if the output torque of the motor  21  provided in the winch  100  is 0, or greater than a maximum permissible torque (at S 12 ), transmitting a command to stop at software level from a control unit  400 , if it is determined via the safety logic that the length of the wire  11  exceeds the preset safe length range (at S 1 ), determining a permissible length in which a limit switch  6  mechanically determines if the length of the wire  11  exceeds the preset permissible length range (at S 13 ), receiving the command to stop at software level from the control unit  400 , if it is determined via the safety logic that the output torque of the motor  21  is 0 or greater than the maximum permissible torque (at S 1 ), stopping the driving of the winch  100  according to operation state of the motor  21  which is stopped in response to the command to stop at software level (at S 4 ), and stopping the driving of the winch  100  by the limit switch  6  which mechanically blocks power supply to the motor  21  and operates the brake module  3  (at S 5 ). 
     The safety logic may be a local safety logic mentioned when explaining the winch  100 , or the safety logic mentioned when explaining the winch safety system  1000 . 
     The determining of the safe length (at S 11 ) may precede the determining of the motor power (at S 12 ). These two operations may be performed in certain order, because when performed concurrently, difficulty may arise in determining a direction of implementing the operations. 
     Further, the winch safety control method may additionally include stopping the driving of the winch  100  by an emergency switch for mechanically detecting emergency state and operating accordingly, which blocks power supply to the motor  21  and operates the brake module  3  (at S 3 ), in which the emergency may arise due to a power failure, a problem in the safety logic which results in a problem in the determination of length of the wire  11  or a size of output torque of the motor  21 , or a problem in the control unit  400 , the limit switch  6  or the motor  21  which results in abnormality in the controlling of the length of the wire  11 . The emergency switch may be a power-failure switch which determines power failure. 
     The three dimensional wire flying system according to the present invention may be used in performances or plays at theatres. 
     While the present 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.