Patent Publication Number: US-2010121489-A1

Title: Robot and robot system

Description:
BACKGROUND 
     1. Technical Field 
     The present invention relates to a robot, a robot system, and the like. The invention especially relates to position detection of a movable portion of the robot. 
     2. Related Art 
     Manufacturing apparatuses using a plurality of robots are widely used to automate tasks. In general, the robots are programmed so as to operate in synchronization with an operation of each robot. Thus, the robots do not collide with each other. In a case where each robot is autonomously operated, it potentially results in a collision with each other. A method for preventing the collision between the robots is disclosed in JP-A-2004-280635. In the method, the collision is prevented by simulating operations of each robot. According to the method, a plurality of models of the robot is formed in a computer so as to presume a transition of major points forming the models. Subsequently, it is examined that whether or not the robot models interfere with each other. In a case where the robot models interfere with each other, one of the robots is stopped for a predetermined time in order to avoid a collision. 
     A method for detecting a location to which a mobile robot moves is disclosed in JP-A-2007-300470. According to the method, the robot moves with a radio frequency identification (RFID) tag or an ultrasonic wave tag. A position of the robot is detected by a reception of a radio wave or an ultrasonic wave at a receiver. 
     In simulating operations of the robot, it is necessary to recognize positions of movable portions, such as arms and hands, included in the robot. Thus, a robot is required that can detect the positions of the movable portions in a short period of time. 
     SUMMARY 
     The invention intends to solve at least part of the above problem, and can be realized by the following aspects. 
     According to a first aspect of the invention, a robot system includes a robot including a movable portion, a plurality of transmitters that is provided on the movable portion and transmits wireless signals, three or more receivers receiving the wireless signals transmitted from each of the transmitters, and a position calculating unit detecting locations of the transmitters based on the wireless signals that the plurality of the receivers receives. In the system, the position calculating unit detects a pose of the robot from information on the locations of the detected plurality of the transmitters. 
     According to the robot system, the wireless signal transmitted from the transmitter is received by the three or more of the receivers. The longer a distance between the transmitter and the receiver, the longer it takes for the receiver to receive the wireless signal. The distance between the transmitter and the receiver can be calculated by multiplying a propagation velocity of the wireless signal by time required for the propagation. Thereafter, a relative position between the transmitter and the receiver can be calculated by a triangulation method. 
     The transmitters are provided on the movable portion of the robot. Thus, by detecting locations of the transmitters, a pose of the robot can be detected. The pose of the robot is detected by providing a sensor, such as an encoder, to a portion where the movable portions are coupled to each other. Then, a relative position between the movable portions is detected. In that case, positional data of one end of each movable portion and positional data of another end of each movable portion are detected, so that it is possible to recognize a relative position of both ends of the movable portion to be coupled. In a case where the robot includes a plurality of the movable portions, a location of the movable portion at a terminal is recognized by adding information on relative positions of each movable portion. With the method according to the first aspect, locations of the transmitters can be directly detected. Therefore, the position calculating unit can detect a position and a pose of the movable portion in a short period time compare with the method in which the position and the pose of the movable portion are calculated by the relative positions between each movable portion. 
     The robot system may further include a conveyor conveying a workpiece and a plurality of transmitters provided on the conveyor. In the system, the position calculating unit may detect a location of the conveyor with the receivers so as to calculate a relative position between the conveyor and the robot. 
     According to the robot system, the position calculating unit calculates a relative position between the conveyor device and the robot. As a result, the robot can recognize a reachable range of the movable portions of the robot with respect to the conveyor device. 
     In the robot system, the position calculating unit may calculate a trajectory of the movable portion. 
     According to the robot system, the position calculating unit can presume inertia force applied to each movable portion using the computed trajectory of the movable portion. 
     In the robot system, the transmitter is an ultrasonic wave tag transmitting an ultrasonic wave while each of the receivers receives the ultrasonic wave. 
     According to the robot system, the distance between the transmitter and the receiver is measured using the ultrasonic waves. Compared with a propagation velocity of electromagnetic waves such as light and radio waves, a propagation velocity of the ultrasonic waves is slower. Therefore, the ultrasonic waves have a longer propagation time than the electromagnetic waves. As a result, arrival time of the ultrasonic waves can be easily measured compared with the case of using the electromagnetic waves. 
     In the robot system, the number of transmitters provided on the movable portion may be equal to or larger than the number of degrees of freedom at the movable portion. 
     According to the robot system, a location to which the movable portion moves can be detected corresponding to the number of degrees of freedom at the movable portion. 
     The robot system may further include a simulation calculating unit calculating a transition of the trajectory of the movement of the movable portion. In the system, the simulation calculating unit may calculate the transition of the trajectory of the movement using the locational information on the transmitters. 
     According to the robot system, a pose of the movable portion can be recognized from the locational information on the transmitter. Then, the transition of the movable portion is calculated from the pose. The transition of the movable portion is computed based on the position of the movable portion before the transition. As a result, the transition of the movable portion can be accurately computed. 
     According to a second aspect of the invention, a robot system includes a plurality of robots operating in the robot system, a plurality of transmitters that is provided on a movable portion of each of the robots and transmits wireless signals, three or more receivers receiving the wireless signals transmitted from each of the transmitters, a position calculating unit detecting locations of the transmitters based on the wireless signals that the plurality of the receivers receives, and a collision calculating unit presuming whether or not the robots collide with each other. In the system, the collision calculating unit detects a collision between the robots using information on the locations of the transmitters. 
     According to the robot system, the locations of the transmitters can be detected in a short period of time. The collision calculating unit detects a collision between the robots using the locational information on the transmitters. As a result, the collision between the robots can be detected in a short period of time. 
     In the robot system, the transmitter may be an ultrasonic wave tag transmitting an ultrasonic wave while each of the receivers may receive the ultrasonic wave. 
     According to the robot system, the distance between the transmitter and the receiver is measured using the ultrasonic waves. Compared with a propagation velocity of electromagnetic waves such as light and radio waves, a propagation velocity of the ultrasonic waves is slower. Therefore, the ultrasonic waves have a longer propagation time than the electromagnetic waves. As a result, arrival time of the ultrasonic waves can be easily measured compared with the electromagnetic waves. 
     In the robot system, the collision calculating unit may include a simulation calculating unit calculating a transition of a trajectory of a movement of the movable portion and an interference calculating unit calculating whether or not the movable portion of each of the robot interfere with each other. 
     According to the robot system, the simulation calculating unit calculates the transition of the movable portion. Then, the collision calculating unit calculates whether or not the movable portions collide with each other. As a result, it is possible to detect a collision between the movable portions at each location during the movement of the movable portions. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be described with reference to the accompanying drawings, wherein like numbers reference like elements. 
         FIG. 1  is a perspective view schematically showing a structure of a robot system. 
         FIG. 2  is a perspective view schematically showing a robot. 
         FIG. 3A  is a sectional view schematically showing a robot ultrasonic wave tag while  FIG. 3B  is a block diagram showing an electric control of the ultrasonic wave tag. 
         FIG. 4  is a block diagram showing an electric control of the robot system. 
         FIG. 5  is a flowchart showing a process of moving a workpiece to storage. 
         FIGS. 6A ,  6 B,  6 C, and  6 D are diagrams showing an operation method using the robot. 
         FIGS. 7A and 7B  are diagrams showing the operation method using the robot. 
         FIGS. 8A and 8B  are diagrams showing the operation method using the robot. 
         FIGS. 9A ,  9 B, and  9 C are diagrams showing the operation method using the robot. 
         FIGS. 10A ,  10 B, and  10 CB are diagrams showing the operation method using the robot. 
     
    
    
     DESCRIPTION OF EXEMPLARY EMBODIMENT 
     Hereinafter, an embodiment of the invention will be described with reference to the accompanying drawings. The scales of members in the drawing are adequately changed so that they can be recognized. 
     Embodiment 
     A robot, a robot system, and a method for controlling the robot according to the embodiment will be described with reference to  FIGS. 1 to 10C . The method for controlling the robot will be described using an example. In the example, two robots move while respectively gripping a workpiece. The robots release the workpiece, so that the workpiece is moved. 
       FIG. 1  is a perspective view schematically showing a structure of the robot system. As shown in  FIG. 1 , a robot system  1  mainly includes a conveyor device  2  serving as a conveyer, a position detecting unit  3 , and a robot  4 . The conveyor device  2  includes a base  5  formed long in one direction. A longitudinal direction of the base  5  is referred to as an X direction. A direction opposite to the gravity direction is referred to as a Z direction while a direction orthogonal to the X and Y directions is referred to as a Y direction. 
     Provided on both sides of the base  5  in the Y direction is a pair of side plates  6 . Provided on both ends in the X direction of upper surfaces of each side plate  6  are workpiece ultrasonic wave tags  7  serving as a transmitter and an ultrasonic wave tag. Further, provided on the upper surface of the side plate  6 , which is a side adjacent to the robot  4 , is a radio wave transmitting device  8 . Each of the workpiece ultrasonic wave tags  7  includes an ultrasonic wave generating source inside thereof, being able to transmit ultrasonic waves serving as a wireless signal. Locations of the workpiece ultrasonic wave tags  7  installed on each side plate  6  are detected so that positions of the side plates  6  can be recognized. The radio wave transmitting device  8  includes a transmission circuit and an antenna, being able to transmit radio signals having a predetermined waveform. 
     Provided between the two side plates  6  is a belt  9 . The belt  9  is a sheet formed in a cylindrical shape and includes a pulley inside thereof (not shown). A predetermined tension is applied to the belt  9  in the X direction by the pulley. A motor  10  is provided on a surface of the side surface  6 , which is adjacent to the robot  4 , in the left when viewed from the robot  4 . A drive shaft of the motor  10  is coupled to the pulley. Placed on the upper surface of the belt  9  are workpieces  11 , and each of the workpieces  11  is supported by a workpiece support  12 . A plurality of the workpiece ultrasonic wave tags  7  is provided on the workpiece support  12 . The workpiece  11  is placed on the belt  9  by a supply device that is not shown. It is possible to move the workpiece  11  in the X direction via the belt  9  by driving the motor  10 . 
     A relative positional relation between the side plates  6  and the belt  9  is set in advance. The robot system  1  can recognize a location of the belt  9  by detecting locations of the workpiece ultrasonic wave tags  7  provided on the side plates  6 . Accordingly, the robot system  1  can recognize a flow direction of the workpiece  11  as well as a movable range of the workpiece  11 . 
     Two of the robots  4  are provided in the right when the conveyor device  2  is viewed in the X direction and in the right when the conveyor device  2  is viewed in the Y direction. The robot  4  positioned on a side opposite to the X direction is referred to as a first robot  4   a.  The robot  4  positioned on a side in the X direction is referred to as a second robot  4   b.  The robot  4  is provided nearby the belt  9 , being able to grip the workpiece  11  on the belt  9 . Provided on the robot  4  is a plurality of robot ultrasonic wave tags  13  serving as a transmitter and a ultrasonic wave tag. 
     Two first struts  14  are vertically arranged in the Z direction at a side surface in the Y direction with respect to the conveyor device  2 . Provided on the first struts  14  is a first receiving device support  15 . The outline of the first receiving device support  14  is an almost rectangular shape by braces. The first receiving device support  15  includes two braces  15   a  provided inside thereof, so that the first receiving device support  15  includes three rectangular windows  15   b  formed therein. Provided to the braces corresponding to each side of the three windows  15   b  are workpiece ultrasonic wave receiving devices  16 . Each of the workpiece ultrasonic wave receiving devices  16  receives ultrasonic wave signals. The workpiece ultrasonic wave receiving device  16  is provided so as to oppose the conveyor device  2 . The workpiece ultrasonic wave receiving device  16  is placed above the belt  9 , being able to receive ultrasonic wave signals transmitted from the workpiece ultrasonic wave tag  7 . The workpiece ultrasonic wave receiving devices  16  are arranged in a predetermined layout. Accordingly, three or more of the workpiece ultrasonic waver receivers  16  receive the ultrasonic wave signals transmitted from the single workpiece ultrasonic wave tag  7 . 
     Two second struts  17  are arranged vertically on the first receiving device support  15 . Provided on the second struts  17  are second receiving device supports  18 . The second receiving device supports  18  are provided so as to extend in the direction opposite to the Y direction. Thus, the second receiving device supports  18  reach above the robot  4 . The second receiving device supports  18  are cross-linked to each other in the X direction above the robot  4 . Provided to the second receiving device supports  18  are robot ultrasonic wave receiving devices  19 , serving as a receiver, so as to oppose the robot  4 . Three robot ultrasonic wave receiving devices  19  are provided above each robot  4 . Each of the ultrasonic wave receiving devices  19  can receive ultrasonic wave signals transmitted from the robot ultrasonic wave tag  13 . 
     Provided in the Y direction with respect to the conveyor device  2  is as a storage device  20 . By changing a pose, the robot  4  can move the workpiece  11  placed on the belt  9  to above the storage device  20 . The storage device  20  includes a lifting mechanism therein, lowering the upper surface thereof in accordance with the amount of the workpiece  11 . The storage device  20  moves an area to which the workpiece  11  to be placed to the same level as the belt  9 . 
     Provided in the X direction with respect to the robot  4  is a control device  21 . The control device  21  controls the robot system  1  including the conveyor device  2 , the position detecting unit  3 , the robot  4 , and the like. 
       FIG. 2  is a perspective view schematically showing the robot. As shown in  FIG. 2 , the robot  4  includes a base  24 . On the base  24 , a rotation base  25  serving as a movable portion is provided. The rotation base  25  includes a fixed base  25   a  and a rotation axis  25   b.  The rotation base  25  includes a servomotor and a speed reduction mechanism therein, being able to rotate and stop the rotation axis  25   b  with angular accuracy. Provided on the fixed base  25   a  are the robot ultrasonic wave tags  13 . By using the workpiece ultrasonic wave receiving device  16 , locations of the workpiece ultrasonic wave tags  7  provided on the upper surfaces of the side plates  6  of the conveyor device  2  and locations of the robot ultrasonic wave tags  13  provided on the rotation base  25  are detected. Accordingly, it is possible to set data of a relative position between the conveyor device  2  and the robot  4 . This allows the robot  4  to recognize a range in which the workpiece  11  flowing on the belt  9  can be captured. 
     A first joint  26  serving as a movable portion is provided in connection with the rotation axis  25   b  of the rotation base  25 . A first arm  27  serving as a movable portion is provided in connection with the first joint  26 . The robot ultrasonic wave tag  13  is provided on the rotation axis of the first joint  26 . By detecting a position of this robot ultrasonic wave tag  13 , a rotation angle when rotating the rotation axis  25   b  can be detected. A second joint  28  serving as a movable portion is provided in connection with the first arm  27 . The robot ultrasonic wave tag  13  is provided on the rotation axis of the second joint  28 . By detecting a position of this robot ultrasonic wave tag  13 , a pose of the first arm  27  can be detected the first joint  26  as a center. 
     A second arm  29  serving as a movable portion is provided in connection with the second joint  28 . The second arm  29  includes a fixed axis  29   a  and a rotation axis  29   b.  The second arm  29  can rotate the rotation axis  29   b  about a longitudinal direction of the second arm  29 . A third joint  30  is provided in connection with the rotation axis  29   b  of the second arm  29 . A pair of the robot ultrasonic wave tags  13  is provided on both ends of the third joint  30  in a rotation axis direction thereof. By detecting positions of these robot ultrasonic wave tags  13 , a pose of the second arm  29  and a rotational state of the rotation axis  29   b  can be detected. 
     A third arm  31  serving as a movable portion is provided in connection with the third joint  30 . The third arm  31  includes a fixed axis  31   a  and a rotation axis  31   b.  The third arm  31  can rotate the rotation axis  31   b  about a longitudinal direction of the third arm  31 . A hand  32  serving as a movable portion is provided in connection with the rotation axis  31   b  of the third arm  31 . The hand  32  is formed long in a direction orthogonal to the rotation axis  31   b  of the third arm  31 . The robot ultrasonic wave tags  13  are provided on both ends in a longitudinal direction of the hand  32 . By detecting positions of these robot ultrasonic wave tags  13 , a pose of the hand  32  can be detected. 
     Provided to the hand  32  is a pair of fingers  33  serving as a movable portion. The hand  32  includes a servomotor and a linear moving mechanism driven by the servomotor. The linear moving mechanism can change an interval between the fingers  33 . 
     The first joint  26 , the second joint  28 , the second arm  29 , the third joint  30 , and the third arm  31  respectively includes a servomotor and a speed reduction mechanism therein, so that they can rotate and stop the first, second, and third arms  27 ,  29 , and  31  with angular accuracy. As described above, the robot  4  includes many joints and rotation mechanisms. In addition to the joints and the rotation mechanisms, controlling the fingers  33  enables the robot  4  to grip the workpiece  11 . 
     The number of the robot ultrasonic wave tags  13  provided to the first arm  27 , the second arm  29 , the third arm  31 , and the hand  32  is equal to or larger than the number of degrees of freedom that each portion can operate. Thus, it is possible to detect poses of each portion. 
       FIG. 3A  is a sectional view schematically showing the robot ultrasonic wave tag. As shown in  FIG. 3A , the robot ultrasonic wave tag  13  includes a support  34 . Coupled to the support  34  is an exterior  35  having a sphere shape. The exterior  35  includes a cavity formed therein. The exterior  35  may be made of any material as long as ultrasonic waves can pass through the material. For example, the exterior  35  may be made of a hard resin or the like. 
     Provided below the exterior  35  is a power transmitting unit  36 . The power transmitting unit  36  includes a core  36   a,  a coil  36   b,  and the like. The coil  36   b  is wound around the core  36   a.  By energizing an alternating current to the coil  36   b,  magnetic lines are formed in the core  36   a.  Then, it is possible to form a circuit of the formed magnetic lines toward the inside of the exterior  35 . 
     Provided inside of the exterior  35  is a body  37  having a sphere shape. A space is formed between the body  37  and the exterior  35 . The space includes a fluid  38  which is lubricious and a gas  39 . Therefore, the body  37  easily moves within the exterior  35 . The fluid  38  preferably is a material having low viscosity. In the present embodiment, a silicone oil is employed, for example. 
     Provided at the upper portion of the body  37  is an ultrasonic wave outputting unit  40 . The ultrasonic wave outputting unit  40  includes a vibration plate  41 , a piezoelectric element  42  fixed to the vibration plate  41 , and the like. The piezoelectric element  42  is driven and the vibration plate  41  is vibrated, so that ultrasonic waves can be transmitted from the vibration plate  41 . 
     The ultrasonic waves transmitted from the robot ultrasonic wave tag  13  spread in a cone and proceed. A spread angle and a frequency when the ultrasonic waves spread differ depending on the specification of the ultrasonic wave outputting unit  40 . Thus, the spread angle and the frequency are not specifically limited. In the present embodiment, the spread angle is set to be about 100 degrees, for example. A frequency close to 40K Hz is employed for the frequency of the ultrasonic waves. 
     Provided below the ultrasonic wave outputting unit  40  is a circuit substrate  43 . The piezoelectric element  42  and the circuit substrate  43  are electrically coupled with a wiring line  44 . Provided to the left of the circuit substrate  43  in the drawing is an antenna  45 . The antenna  45  and the circuit substrate  43  are electrically coupled with the wiring line  44 . 
     Provided below the circuit substrate  43  is a power receiving unit  46 . The power receiving unit  46  includes a core  46   a,  a coil  46   b,  and the like. The coil  46   b  is wound around the core  46   a.  When the power receiving unit  46  is opposed to the power transmitting unit  36 , magnetic lines are outputted from the core  36   a  of the power transmitting unit  36 . The outputted magnetic lines pass through the core  46   a  of the power receiving unit  46 . Accordingly, a transformer is formed by the power transmitting unit  36  and the power receiving unit  46 . 
     Provided at the lower portion of the body  37  is a plummet  47 . The plummet  47  is made of a material whose specific gravity is greater than the body  37 . Gravity acts on the plummet  47 , thereby force in a gravity acceleration direction acts on the plummet  47 . The body  37  is rotatably provided in the exterior  35 . Therefore, regardless of the facing direction of the support  34  of the robot ultrasonic wave tag  13 , the ultrasonic output unit  40  faces in the Z direction. Provided in the Z direction with respect to the robot  4  are robot ultrasonic wave receiving devices  19 . As a result, each of the robot ultrasonic wave receiving devices  19  can receive the ultrasonic waves transmitted from the ultrasonic wave outputting unit  40 . 
       FIG. 3B  is a block diagram showing an electric control of the ultrasonic wave tag. As shown in  FIG. 3B , the robot ultrasonic wave tag  13  includes the antenna  45 . The antenna  45  is coupled to a receiving circuit  50 . The receiving circuit  50  amplifies weak radio waves that the antenna  45  receives. Then, the antenna  45  and the receiving circuit  50  receive the radio signals transmitted from the radio wave transmitting device  8 . The receiving circuit  50  is coupled to a code analyzing circuit  51 . The code analyzing circuit  51  analyzes the radio signals transmitted from the radio wave transmitting device  8 . Each of the radio signals includes a code signal and a transmission timing signal. The code analyzing circuit  51  analyzes the code signal so as to determine whether or not to transmit ultrasonic waves. A code of the code signal indicates an identification number. Each robot ultrasonic wave tag  13  has a code set in advance. The code analyzing circuit  51  determines whether or not the received code signal matches with the code set in the robot ultrasonic wave tag  13 . When the received code signal matches with the code set in the robot ultrasonic wave tag  13 , the code analyzing circuit  51  determines to transmit ultrasonic waves. 
     The code analyzing circuit  51  is coupled to a sending controlling circuit  52 . The sending controlling circuit  52  is coupled to a transmission signal forming circuit  53  and a sending circuit  54 . The transmission signal forming circuit  53  includes an oscillation circuit and forms voltage signals having a predetermined waveform. The waveform pattern is not specifically limited and a sine wave, a square wave, a triangle wave, or the like can be used. In the present embodiment, the sine wave is employed, for example. A frequency of the waveform is not limited to one kind. A plurality kinds of waveforms of a frequency may be formed. In a case where only one kind of waveform is used, the plurality kinds of waveforms of a frequency are not necessarily formed. The transmission signal forming circuit  53  outputs the formed voltage signals to the sending controlling circuit  52 . 
     The sending controlling circuit  52  controls sending of signals. When the code analyzing circuit  51  determines to transmit ultrasonic waves, the transmission signal forming circuit  53  outputs the formed voltage signals to the sending circuit  54 . Then, the transmission signal forming circuit  53  outputs the voltage signal in synchronization with the transmission timing signal. The sending circuit  54  includes an amplifier and the ultrasonic wave outputting unit  40 . The amplifier amplifies the inputted voltage signals and outputs the voltage signals to the ultrasonic wave outputting unit  40 . The ultrasonic wave outputting unit  40  includes the vibration plate  41  having the piezoelectric element  42  and the like, and vibrates the vibration plate  41  corresponding to the voltage signal. The vibration plate  41  vibrates the gas, allowing the ultrasonic wave outputting unit  40  to transmit ultrasonic waves. 
     The robot ultrasonic wave tag  13  includes a power supply unit  55 . For the power supply unit  55 , a battery, a secondary battery or the like can be used. In the present embodiment, a lithium secondary battery is employed for the power supply unit  55 , for example. The power supply unit  55  supplies electric power to each circuit included in the robot ultrasonic wave tag  13 . 
     The power supply unit  55  is electrically coupled to the power receiving unit  46 . The power receiving unit  46  and the power transmitting unit  36  can form a transformer. The power transmitting unit  36  is electrically coupled to a main power supply unit  56 . Electric power is supplied from the main power supply unit  56  to the power supply unit  55  through the power transmitting unit  36  and the power receiving unit  46 . 
     The antenna  45 , the receiving circuit  50 , the code analyzing circuit  51 , the sending controlling circuit  52 , the transmission signal forming circuit  53 , the sending circuit  54 , the power supply unit  55 , and the power receiving unit  46  are provided in the body  37 . Then, the antenna  45  receives signals and electric power by air from the exterior of the body  37 . 
     That is, the robot ultrasonic wave tag  13  receives radio signals. The robot ultrasonic wave tag  13  transmits ultrasonic waves when the identification code signal included in the radio signal matches with the identification code set in advance in the robot ultrasonic wave tag  13 . At this time, the robot ultrasonic wave tag  13  transmits the ultrasonic wave in synchronization with the transmission timing signal included in the radio signal. 
     The workpiece ultrasonic wave tag  7  has the similar circuit structure as the robot ultrasonic wave tag  13 . Therefore, the workpiece ultrasonic wave tag  7  has the similar functions as the robot ultrasonic wave tag  13 . The workpiece ultrasonic wave tag  7  transmits ultrasonic waves when the identification code signal included in the radio signal matches with the identification code set in advance in the workpiece ultrasonic wave tag  7 . At this time, the workpiece ultrasonic wave tag  7  transmits the ultrasonic wave in synchronization with the transmission timing signal included in the radio signal. 
       FIG. 4  is a block diagram showing an electric control of the robot system. Referring to  FIG. 4 , the control device  21  serving as a controller of the robot system  1  includes a central processing unit (CPU)  59  executing various calculation processes as a processor and a memory  60  serving as a storing unit storing various pieces of information. 
     A conveyor driving device  61 , the radio wave transmitting device  8 , the workpiece ultrasonic wave receiving device  16 , the robot ultrasonic wave receiving device  19 , a robot driving device  62 , and the storage device  20  are coupled to the CPU  59  through an input/output interface  63  and a data bus  64 . Further, an input device  65  and a display  66  are also coupled to the CPU  59  through the input/output interface  63  and the data bus  64 . 
     The conveyor driving device  61  is coupled to the conveyor device  2  so as to control the conveyor device  2 . The conveyor driving device  61  controls a movement and a stop of the belt  9  as well as a speed of the movement. The robot driving device  62  is coupled to the first and second robots  4   a  and  4   b  so as to control operations of the robot  4 . The robot driving device  62  outputs information on pose of the robot  4  to the CPU  59 . The robot  4  can move the hand  32  to a location specified by the CPU  59  and operate the finger  33 . 
     The input device  65  inputs the code of the workpiece ultrasonic wave tag  7  and that of the robot ultrasonic wave tag  13  as well as behavior conditions such as a gripping method when the robot  4  grips the workpiece support  12 . For example, the input device  65  receives coordinates indicating a shape of the workpiece support  12  of each workpiece  11  from an exterior device (not shown) and inputs the coordinates thereto. The display  66  displays data on the workpiece  11  and the robot ultrasonic wave tag  13  as well as operation states. Based on the information displayed on the display  66 , operators perform input operations with the input device  65 . 
     The memory  60  includes a semiconductor memory, such as RAMs and ROMs, and an external memory device, such as hard disks and DVD-ROMs. From a functional point of view, the memory  60  has a storage area storing program software  67  in which a controlling procedure of operations of the robot system  1  is described. In addition, the memory  60  has a storage area storing ultrasonic wave tag data  68  which is information such as the codes set in the workpiece ultrasonic wave tag  7  and the robot ultrasonic wave tag  13 . In the ultrasonic wave tag data  68 , a location where the robot ultrasonic wave tag  13  is provided and a relation with the codes of the robot ultrasonic wave tag  13  are stored. The memory  60  has a storage area storing robot-related data  69  which is information on a relative position between the conveyor device  2  and the robot  4 , a relative position between the position detecting unit  3  and the robot  4 , a relative position between the storage device  20  and the robot  4 , and the like. The memory  60  has a storage area storing workpiece data  70  which is data on a shape of the workpiece  11 , a location at which the fingers  33  of the robot  4  grip the workpiece  11 , and the like. In addition, the memory  60  has a storage area serving as a work area or a temporary file for the CPU  59 , and other various storage areas. 
     The CPU  59  performs identification of the workpiece  11  and control for moving the workpiece  11  in accordance with the program software  67  stored in the memory  60 . As a specific function realization unit, the CUP  59  includes a robot controlling unit  71  performing control for moving the workpiece  11  by driving the robot  4 . Further, the CPU  59  includes a transmission controlling unit  72  performing control of the radio wave transmitting device  8  so that specific workpiece ultrasonic wave tags  7  and the robot ultrasonic wave tags  13  transmit ultrasonic waves. The CPU  59  includes a transmission position calculating unit  73  serving as a position calculating unit calculating locations of the workpiece ultrasonic wave tag  7  and the robot ultrasonic wave tag  13  with the ultrasonic waves that the workpiece ultrasonic receiving device  16  and the robot ultrasonic wave receiving device  19  receive. The CPU  59  also includes a collision calculating unit  74  detecting a collision between the movable portion of the first robot  4   a  and the movable portion of the second robot  4   b.  The collision calculating unit  74  includes a simulation calculating unit  75  serving as a trajectory calculating unit, an interference calculating unit  76 , and the like. The simulation calculating unit  75  simulates operations of the arms and the hand  32  of the robot  4 . The interference calculating unit  76  calculates whether or not the movable portion of the first robot  4   a  interferences with the movable portion of the second robot  4   b  using the calculated result of the simulation. In addition, the CPU  59  includes a conveyor controlling unit  77  controlling operations of the belt  9  together with the operations of the robot  4 , and the like. 
     Method for Controlling Robot 
     A method for controlling the robot will be described with reference to  FIGS. 5 to 10C . In the method, the robot is controlled during an operation of moving the workpiece  11  from the conveyor device  2  to the storage device  20  by using the above-described robot system  1 .  FIG. 5  is a flowchart showing a process of moving the workpiece to the storage.  FIGS. 6A to 10C  are diagrams showing an operation method using the robot. 
     In the flowchart of  FIG. 5 , step S 1  is simultaneously performed with steps S 2  to S 7 . The step S 1  corresponds to a first moving step. In the step, the workpiece is moved by the conveyor device. The step goes to step S 9 . The steps S 2  and S 3  are simultaneously performed. The step S 2  corresponds to a workpiece detecting step. In the step, a location of the workpiece is detected by receiving the ultrasonic waves transmitted from the workpiece ultrasonic wave tag. The step goes to step S 4 . The step S 3  corresponds to a robot detecting step. In the step, locations of each portion included in the robot are detected by receiving the ultrasonic waves transmitted from the robot ultrasonic wave tag. The step goes to the step S 4 . The step S 4  corresponds to a simulation step. In the step, a location to which the workpiece moves is predicted, and a trajectory of the hand of the robot when moving the hand to the location is simulated. Additionally, a trajectory of the workpiece when moving the workpiece to the storage is simulated in the step. The step goes to step S 5 . The step S 5  corresponds to a collision calculating step. In the step, it is calculated that whether or not the two robots collide with each using the simulation result of the trajectory of each movable portion of the robot. The step goes to step S 6 . 
     The step S 6  corresponds to a collision determining step. In the step, it is determined that whether or not the two robots collide with each other. The step goes to step S 7  in a case where portions of the robots collide with each other. The step goes to the step S 8  in a case where no portions of the robots collide. The step S 7  corresponds to a plan changing step. In the step, an operation plan of the robot is changed. The step goes to the step S 4 . The step S 8  corresponds to a second moving step. In the step, the robot moves the workpiece to the storage device. The step goes to the step S 9 . The step S 9  corresponds to an end confirming step. In the step, it is confirmed that whether or not all workpieces are flown. If there still is the workpiece to be flown and the operation is not completed, the step goes to the steps  1 ,  2 , and  3 . If there is no workpiece to be flown and the operation is completed, the process of moving the workpiece to the storage is completed. 
     The operation method using the robot corresponding to the steps shown in  FIG. 5  will be described in detail with reference to  FIGS. 6A to 10C .  FIG. 6A  corresponds to the first moving step of the step  1 . As shown in  FIG. 6A , the workpiece  11  is placed on the belt  9  in the step  1 . The workpiece  11  is moved by the belt  9 . 
       FIGS. 6B ,  6 C,  6 D,  7 A, and  7 B correspond to the workpiece detecting step of the step S 2 . As shown in  FIG. 6B , the radio wave transmitting device  8  outputs radio signals  79 . A plurality kinds of the workpieces  11  is placed on the belt  9 . The radio signals  79  are emitted toward the workpiece  11 . The workpiece ultrasonic wave tag  7  has an identification code set therein. The radio signal  79  includes the identification code and the transmission timing signal used for transmitting ultrasonic waves. The radio wave transmitting device  8  switches the identification code and sequentially sends the radio signals  79 . A pair of the workpiece ultrasonic wave tags  7  is provided on one side of the workpiece  11 . The pair of the workpiece ultrasonic wave tags  7  is referred to as a first workpiece ultrasonic wave tag  7   a  and a second workpiece ultrasonic wave tag  7   b.  The workpiece ultrasonic wave tag  7  receives the radio signals  79 . 
     As shown in  FIG. 6C , the first workpiece ultrasonic wave tag  7   a  transmits ultrasonic wave signals  80  serving as a wireless signal and an ultrasonic wave when the identification code included in the radio signal  79  matches with the identification code set in the first workpiece ultrasonic wave tag  7   a.  The ultrasonic wave signals  80  transmitted in the Z direction from the first workpiece ultrasonic wave tag  7   a  are received by three of the workpiece ultrasonic wave receiving devices  16 . The transmission controlling unit  72  detects the time elapsed between the transmission of the ultrasonic wave signal  80  from the first workpiece ultrasonic wave tag  7   a  and the reception of the ultrasonic wave signal  80  at each workpiece ultrasonic wave receiving device  16 . Then, the transmission controlling unit  72  stores the time elapsed in the memory  60 . 
     The time elapsed is detected by detecting amplitude of the ultrasonic wave signal  80 , detecting timing that a waveform of the ultrasonic wave signal  80  corresponds to a waveform of a reference wave by comparing with each other, a phase matching method in which the ultrasonic wave signal  80  having two kinds of frequencies is transmitted so as to detect a phase of the received ultrasonic wave signal  80 , and the like. Since the phase matching method is disclosed in JP-A-2006-242640, the specific description thereof will be omitted. The phase matching method has high measurement accuracy. Thus, with this method, the time elapsed between the transmittance of the ultrasonic wave signal  80  and the reception of the ultrasonic wave signal  80  can be measure with high accuracy. Here, any of the known methods can be used as a detection method. In the present embodiment, the phase matching method is employed, for example. 
     The radio signals  79  are sequentially sent from the radio wave transmitting device  8  to the workpiece ultrasonic wave tag  7 . As shown in  FIG. 6D , the second workpiece ultrasonic wave tag  7   b  transmits the ultrasonic wave signals  80  when the identification code included in the radio signal  79  matches with the identification code set in the second workpiece ultrasonic wave tag  7   b.  The ultrasonic wave signals  80  are received by three of the workpiece ultrasonic receiving devices  16 . The transmission controlling unit  72  detects the time elapsed between the transmission of the ultrasonic wave signal  80  from the second workpiece ultrasonic wave tag  7   b  and the reception of the ultrasonic wave signals at each workpiece ultrasonic wave receiving device  16 . Then, the transmission controlling unit  72  stores the time elapsed in the memory  60 . 
     As shown in  FIG. 7A , three of the workpiece ultrasonic wave receiving devices  16  receive the ultrasonic wave signal  80  transmitted from the first workpiece ultrasonic wave tag  7   a.  The transmission position calculating unit  73  adds the time elapsed between the transmission of the ultrasonic wave signal  80  from the first workpiece ultrasonic wave tag  71  and the reception of the ultrasonic wave signal  80  at each workpiece ultrasonic wave receiving device  16  to the rate of travel of the ultrasonic wave signal  80  so as to calculate distances  81  that are distances between the first workpiece ultrasonic wave tag  7   a  and each workpiece ultrasonic wave receiving device  16 . 
     Locations of the workpiece ultrasonic wave receiving devices  16  in the robot system  1  are measured in advance, and coordinates of the workpiece ultrasonic receiving devices  16  are stored in the robot-related data  69 . The transmission position calculating unit  73  calculates a location of the first workpiece ultrasonic wave tag  7   a  in the robot system  1  by a triangulation method. Subsequently, the transmission position calculating unit  73  calculates a location of the second workpiece ultrasonic wave tag  7   b  by the same method. 
     As shown in  FIG. 7B , a pose of the workpiece  11  is computed. The pose of the workpiece  11  shows a pose angle  82  with respect to a moving direction of the workpiece  11 . In the present embodiment, the moving direction of the workpiece  11  is the X direction. An angle formed by a straight line passing through the first and second workpiece ultrasonic wave tags  7   a  and  7   b  and the X direction is referred to as the pose angle  82 . The midpoint between the first and second workpiece ultrasonic wave tags  7   a  and  7   b  is computed. This midpoint is referred to as a workpiece position  83 . The workpiece position  83  and the pose angle  82  are stored in the memory  60  as the workpiece data  70 . 
       FIGS. 8A and 8B  are diagrams corresponding to the robot detecting step of the step S 3 . As shown in  FIG. 8A , the radio wave transmitting device  8  emits the radio signals  79  toward the robot  4 . The robot ultrasonic wave tag  13  has an identification code set therein in the same manner as the workpiece ultrasonic wave tag  7 . The radio signal  79  includes the identification code and the transmission timing signal used for transmitting ultrasonic waves. The radio wave transmitting device  8  switches the identification code and sequentially sends the radio signals  79 . The robot ultrasonic wave tag  13  receives the radio signals  79 . 
     As shown in  FIG. 8B , the robot ultrasonic wave tag  13  transmits the ultrasonic wave signals  80  when the identification code included in the radio signal  79  matches with the identification code set in the robot ultrasonic wave tag  13 . The robot ultrasonic wave tag  13  transmits the ultrasonic wave signals  80  in the Z direction. Then, the ultrasonic wave signals  80  are received by the robot ultrasonic wave receiving devices  19 . The transmission controlling unit  72  detects the time elapsed between the transmission of the ultrasonic wave signal  80  from the robot ultrasonic wave tag  13  and the reception of the ultrasonic wave signal  80  at each robot ultrasonic wave tag  19 . Then, the transmission controlling unit  72  stores the time elapsed in the memory  60 . 
     In the same manner as the step S 2 , the ultrasonic wave signals  80  transmitted from the robot ultrasonic wave tag  13  are received by three of the robot ultrasonic wave receiving devices  19 . Then, the transmission position calculating unit  73  calculates the distances  81  which are distances between the robot ultrasonic wave tag  13  and each robot ultrasonic wave receiving device  19 . The transmission position calculating unit  73  calculates a location of the robot ultrasonic wave tag  13  by the triangulation method. The transmission position calculating unit  73  stores the locational information on the position of the robot ultrasonic wave tag  13  in the memory  60  as the ultrasonic wave tag data  68 . 
     The radio wave transmitting device  8  makes the robot ultrasonic wave tags  13  provided to the robot  4  sequentially transmit the ultrasonic wave signals  80 . After the robot ultrasonic wave receiving device  19  receives the ultrasonic wave signals  80 , the transmission position calculating unit  73  calculates the location of the robot ultrasonic wave tag  13 . The transmission position calculating unit  73  calculates positions and poses of each movable portion of the robot  4  using the locational information on the robot ultrasonic wave tags  13 . The transmission position calculating unit  73  stores the locations of each robot ultrasonic wave tag  13  in the memory  60  as well as the positions and the poses of each movable portion. 
       FIG. 9A  is a diagram corresponding to the simulation step of the step  4 . An example of simulating operations of the workpiece  11  and the robot  4  is given. As shown in  FIG. 9A , a location to which the workpiece  11  to be moved is presumed in the step S 4 . The belt  9  of the conveyor device  2  moves at a uniform velocity. The location of the workpiece  11  at a given time is detected, so that it is presumed that the workpiece  11  is moved in a moving direction of the belt after a predetermined time. The simulation calculating unit  75  provides models, such as a belt  86 , a storage device  87 , a first robot  88 , a second robot  89 , and a workpiece  90 , in a virtual space. The belt  86  corresponds to the belt  9  of the conveyor device  2  while the storage device  87  corresponds to the storage device  20 . The robot  88  corresponds to the first robot  4   a  while the second robot  89  corresponds to the second robot  4   b.  The workpiece  90  corresponds to the workpiece  11 . Each model is set to have the same size and shape as those of the actual portions. 
     The simulation calculating unit  75  calculates a trajectory of the workpiece  90  moving along with a movement of the belt  86 . Next, the simulation calculating unit  75  calculates an operation of the second robot  89 . The second robot  89  includes a hand  89   a.  The hand  89   a  corresponds to the hand  32 . The simulation calculating unit  75  calculates a trajectory of the hand  89   a  of the second robot  89  moving to the location to which the workpiece  90  to be moved. Then, the simulation calculating unit  75  determines a location at which the hand  89   a  of the second robot  89  grips the workpiece  90 . 
     The simulation calculating unit  75  calculates an operation of the first robot  88 . The first robot  88  simultaneously operates with the second robot  89 . The first robot  88  includes a hand  88   a.  The hand  88   a  corresponds to the hand  32 . The hand  88   a  of the first robot  88  moves the workpiece  90  to the storage device  87  while gripping the workpiece  90 . The simulation calculating unit  75  calculates a trajectory of the movement of the first robot  88 . 
       FIGS. 9B and 9C  are diagrams corresponding to the collision calculating step of the step S 5 . As shown in  FIG. 9B , in the step  5 , the interference calculating unit  76  calculates the operations of the first and second robots  88  and  89 . The interference calculating unit  76  uses the calculated presumed data of the trajectories. The interference calculating unit  70  performs a calculation so that the first and second robots  88  and  89  are simultaneously operated. The interference calculating unit  70  selects portions of the first and second robots  88  and  89  that come close to each other. 
     The first robot  88  includes a motor  88   b.  The motor  88   b  corresponds to a motor (not shown) included in the third joint  30 . The second robot  89  includes fingers  89   b.  The fingers  89   b  correspond to the fingers  33 . For example, a case is described in which the motor  88   b  of the first robot  88  and the fingers  89   b  of the second robot  89  come close to each other. 
     It is calculated that whether or not the portions come close interfere with each other. As shown in  FIG. 9C , a side surface of the fingers  89   b  of the second robot  89  and that is adjacent to the first robot  88  is referred to as a finger side surface  89   c.  It is calculated that whether or not the finger side surface  89   c  interferes with the motor  88   b.  A formula of the finger side surface  89   c  is calculated by a location and a pose of the fingers  89   b.  Since the finger side surface  89   c  is a flat surface, the formula of the finger side surface  89   c  can be shown as aX+bY+cZ+d=0 when a, b, c, and d are coefficients. The formula of the finger side surface  89   c  can be calculated by computing the coefficients using points on the finger side surface  89   c.    
     A side surface of the motor  88   b  is referred to as a motor side surface  88   c.  The motor  88   b  has a cylindrical shape. Then, segments  88   d  on the motor side surface  88   c  in an axial direction of the motor  88   b  are set. The segments  88   d  are set by divining the motor side surface  88   c  into several portions in a periphery direction. Though it is preferable that the segments  88   d  are provided with equal intervals, it is not necessarily limited. An area of the motor side surface  88   c  to be examined in detail may be finely divided. 
     Subsequently, it is calculated that whether or not each segment  88   d  passes through the finger side surface  89   c.  First, a formula of the segments  88   d  is calculated. The formula of the segments  88   d,  which passes through coordinates (x, y, z) and whose directional vector is (l, m, n), can be shown as (X−x)/1=(Y−y)/m=(Z−z)/n. The formula of the segments  88   d  can be calculated by computing the coefficients using the points on the segments  88   d.    
     Coordinates of an intersection, which is a point at the intersection of the segments  88   d  with the finger side surface  89   c,  are calculated from the formula of the segments  88   d  and that of the finger side surface  89   c.  Subsequently, it is calculated that whether or not the intersection is a range within the finger side surface  89   c  and the motor side surface  88   c.  It is determined that the fingers  89   b  and the motor  88   b  interfere with each other when the intersection is within both surfaces of the finger side surface  89   c  and the motor side surface  88   c.  The portions that interfere with each other and the time of the interference are stored in the memory  60  as the robot-related data  69 . 
     In the collision determining step of the step S 6 , it is confirmed that whether or not there is a location at which the first robot  88  and the second robot  89  interfere with each other using the robot-related data  69 . If there is such location, a plan to drive the first and second robots  88  and  89  is changed in the plan changing step of the step  7 . 
       FIGS. 10A ,  10 B, and  10 C are diagrams corresponding to the plan changing step of the step S 7 . As shown in  FIG. 10A , the plan to drive the first and second robots  88  and  89  is changed in the step S 7 . The first robot  88  grips the workpiece  90 . The workpiece  90  moves along with the movement of the belt  86 , and the hand  89   a  of the second robot  89  moves to the workpiece  90 . These operations do not change. The first robot  88  stops during the movement of the second robot  89 . Therefore, a plan that the first robot  88  moves the hand  88   a  to the storage device  87  is changed. 
     As shown in  FIG. 10B , the second robot  89  grips the workpiece  90 . The first robot  88  moves the hand  88   a  toward the storage device  87  and the second robot  89  moves the hand  89   a  toward the storage device  87 . At this time, the first and second robots  88  and  89  move substantially parallel with each other, so that they hardly collide. As a result, as shown in  FIG. 10  C, the first and second robots  88  and  89  respectively move the workpieces  90  to locations facing the storage device  87 . The plan to drive the robot  4  is changed as above. 
     Subsequently, the simulation step of the step S 4  and the collision calculating step of the step S 5  are performed based on the changed plan. After it is confirmed in the collision determining step of the step S 6  that the first and second robots  88  and  89  do not collide with each other, the second moving step of the step S 8  is performed. In the step S 8 , the robot  4  is driven as planned in the plan changing step of the step S 7  so as to move the workpiece  11  to the storage device  20 . As described above, the process of moving the workpiece  11  from the conveyor device  2  to the storage device  20  is completed. 
     According to the embodiment described above, the following advantageous effects are provided. According to the embodiment, the robot ultrasonic wave tags  3  are provided to the hand  32 , the third joint  30 , and the like of the robot  4 . By detecting locations of the robot ultrasonic wave tags  13 , a pose of the robot  4  can be detected. The pose of the robot  4  is detected by proving a sensor, such as an encoder, to a portion where the movable portions are coupled to each other. Then, a relative position between the movable portions is detected. In that case, positional data of one end of each movable portion is added to positional data of another end of each movable portion, so that it is possible to compute relative positional data of both ends of the movable portion to be coupled. Compared with this method, the locations of the robot ultrasonic wave tags  13  are directly detected in the embodiment. As a result, the transmission position calculating unit  73  can detect positions and poses of the hand  32 , the third joint  30 , and the like in a short period of time. 
     According to the embodiment, distances between the robot ultrasonic wave tags  13  and the robot ultrasonic wave receiving devices  19  are measured with the ultrasonic wave signals  80 . Compared with a propagation velocity of electromagnetic waves such as light and radio waves, a propagation velocity of ultrasonic waves is slower. Therefore, the speed of the ultrasonic waves is faster than that of the electromagnetic waves. As a result, arrival time of the ultrasonic waves can be easily measured compared with the case of using the electromagnetic waves. 
     According to the embodiment, the robot ultrasonic wave tags  13  are provided to the first arm  27 , the second arm  29 , and the like corresponding to the number of degrees of freedom at the movable portion. As a result, a location to which the movable portion moves and a pose of the movable position can be detected. 
     According to the embodiment, a pose of the movable portion, such as the hand  32 , is recognized using locational information of the robot ultrasonic wave tags  13 . Then, a calculation is performed for simulating a transition of the movable portion from the pose. The transition of the movable portion is computed based on the position of the movable portion before the transition. As a result, the transition of the movable portion can be accurately computed. 
     According to the embodiment, a position of the robot ultrasonic wave tag  13  can be detected in a short period of time. The interference calculating unit  76  detects a collision between the robots using data on the robot ultrasonic wave tag  13 . As a result, the collision between the robots can be detected in a short period of time. 
     According to the embodiment, the simulation calculating unit  75  performs a calculation for simulating the transition of the movable portion. Then, the interference calculating unit  76  calculates interference between the movable portions. As a result, it is possible to detect a collision between the movable portions at each location during the movement of the movable portions. 
     According to the embodiment, the robot ultrasonic wave tag  13  transmits the ultrasonic wave signals  80  in the Z direction regardless of a pose of the robot  4 . As a result, the robot ultrasonic wave tag  3  can transmit the ultrasonic wave signals  80  toward the robot ultrasonic wave receiving device  19  regardless of poses of the movable portions of the robot  4 . 
     According to the embodiment, the transmission position calculating unit  73  calculates a relative position between the conveyor device  2  and the robot  4 . As a result, the robot  4  can recognize a reachable range of the movable portions of the robot with respect to the conveyor device. 
     Here, the embodiment is not limited to the above-described and various changes and modification can be made. Modifications will now be described. 
     First Modification 
     In the embodiment above, ultrasonic waves are used for measuring a distance between the robot ultrasonic wave tag  13  and the robot ultrasonic wave receiving device  19 . In stead of the ultrasonic waves, waveforms from other media may be used. For example, the distance may be measured by detecting a phase of light using laser light or infrared light. Electromagnetic waves may be used for measuring the distance. The easiest method for measuring the distance may be employed. In this case, locations and poses of each movable portion of the robot  4  can be detected as well. 
     Second Modification 
     In the embodiment above, the workpiece  11  is moved to the storage device  20  together with the workpiece support  12 . The workpiece support  12  may be left on the belt  9  so that only the workpiece  11  is moved to the storage device  20 . A detachment mechanism may be provided to the workpiece support  12 . In that case, the detachment mechanism may be operated by the hand  32 . This enables operations in the following step to be easily performed. 
     Third Modification 
     In the embodiment above, the radio wave transmitting device  8  sends radio signals to the robot ultrasonic wave tag  13 . The radio wave transmitting device  8  may be replaced with an optic communications device, and the optic communications device may perform optical communication with the robot ultrasonic wave tag  13 . This makes it possible to reduce the effect of electromagnetic noise. 
     Fourth Modification 
     In the embodiment above, a location of the robot ultrasonic wave tag  13  is calculated by the ultrasonic wave signals  80  received by three of the robot ultrasonic wave receiving devices  19 . Four of the robot ultrasonic wave receiving devices  19  may be provided to the single robot  4 . Then, the location of the robot ultrasonic wave tag  13  may be calculated by the ultrasonic wave signals  80  received by the four robot ultrasonic wave receiving devices  19 . A method for calculating a location of an ultrasonic wave source is disclosed in JP-A-6-222130. In the method, one of the ultrasonic wave source and four ultrasonic sonic wave receiving devices are used. Four equations are formed according to distances between the ultrasonic wave source and the four ultrasonic wave receiving devices. The location of the ultrasonic wave source is computed by obtaining solutions to the equations. This method may be employed for computing the location of the robot ultrasonic wave tag  13 . Since this method may not require the transmission timing signals that the radio wave transmitting device  8  transmit, a structure of the circuit can be simplified. 
     Fifth Modification 
     In the embodiment above, the radio wave transmitting device  8  sequentially switches the identification code and sends the radio signals  79  in the robot detecting process of the step S 3 . After receiving the radio signals  79 , the robot ultrasonic wave tag  13  transmits the ultrasonic wave signals  80 . The procedure may not be limited to this. After a lapse of predetermined time from the transmission of the ultrasonic wave signals  80  from one of the robot ultrasonic wave tags  13 , the ultrasonic wave signals  80  may be sequentially transmitted from the rest of the robot ultrasonic wave tags  13 . Since the procedure is simplified, the program software  67  can be simplified as well. As a result, the program software  67  can be manufactured with high efficiency. 
     Sixth Modification 
     In the embodiment above, the workpiece  11  is moved by the conveyor device  2 . However, the method of moving the workpiece  11  is not limited to this. It is only required that the workpiece  11  can move along a predetermined course. For example, a self-propelled device may be provided to the workpiece support  12 . This enables the workpiece  11  to be easily moved between the steps. 
     Seventh Modification 
     Though in the embodiment above, the workpiece  11  is moved straight ahead by the belt  9  of the conveyor device  2 , it is not limited to this. The workpiece  11  may be moved in a curve by the belt  9 . Further, the workpiece  11  may turn at a predetermined angle and proceed. Also in this case, when a trajectory of the movement of the workpiece  11  is presumed in advance, the simulation calculating unit  75  can simulate operations of the workpiece  11  and the robot  4 . 
     Eighth Modification 
     In the embodiment above, the robot  4  grips the workpiece  11  while the workpiece  11  is moved by the belt  9  in the second moving step of the step S 8 . However, the belt  9  may be stopped when the robot  4  grips the workpiece  11 . This enables the robot  4  to easily grip the workpiece  11 . 
     Ninth Modification 
     In the embodiment above, the robot ultrasonic wave tag  13  transmits the ultrasonic wave signals  80 . A frequency transmitted from the ultrasonic wave signal  80  may be varied with respect to each robot ultrasonic wave tag  13 . For example, a frequency analyzing circuit is added to the robot ultrasonic wave receiving device  19 . Then, the robot ultrasonic wave receiving device  19  analyzes the frequency of the ultrasonic wave signal  80 . Accordingly, the robot ultrasonic wave receiving device  19  can recognize the robot ultrasonic wave tag  13  from which the ultrasonic wave signals  80  are transmitted. 
     Tenth Modification 
     In the embodiment above, the transmission position calculating unit  73  calculates positions and poses of each movable portion of the robot  4  using locational information on the robot ultrasonic wave tags  13 . The transmission position calculating unit  73  may calculate movement trajectories of each movable portion. The transmission position calculating unit  73  stores locations of the robot ultrasonic wave tags  13  in the memory  60 . The transmission position calculating unit  73  regenerates the past locational data of the robot ultrasonic wave tags  13  stored in the memory  60 . The transmission position calculating unit  73  calculates the movement trajectories of each movable portion with the data. The transmission position calculating unit  73  may simulate operations of each movable portion in view of inertia force applied to each movable portion from the information on the trajectories of each movable portion. As a result, each movable portion can be simulated with high accuracy. 
     Eleventh Modification 
     In the embodiment above, the transmission position calculating unit  73  calculates positions and poses of each movable portion of the robot  4  using locational information on the robot ultrasonic wave tags  13 . The transmission position calculating unit  73  may detect vibrations of each movable portion by operations of the robot ultrasonic wave tag  13 . When the movable portion of the robot  4  vibrates unwantedly, instructions for maintaining the robot  4  may be displayed in the display  66 . Accordingly, is it possible to know the appropriate maintenance time of the robot  4 . By maintaining the robot  4 , the robot  4  can be operated with high quality. 
     Twelfth Modification 
     In the embodiment above, the workpiece ultrasonic wave receiving device  16  is provided to the first receiving device support  15  while the robot ultrasonic wave receiving device  16  is provided to the second receiving device support  18 . The workpiece ultrasonic receiving device  16  may not be directly coupled to the conveyor device  2 . The robot ultrasonic wave receiving device  19  may be coupled to the second receiving device support  18  with no member having rigidity interposed therebetween. The workpiece ultrasonic receiving device  16  and the robot ultrasonic wave receiving device  19  may be installed on the ceiling of the room where the robot system  1  is provided. The transmission position calculating unit  73  may detect a location of the conveyor device  2  and a location of the robot  4  so as to recognize a relative position between the conveyor device  2  and the robot  4 . Also in this case, the relative position between the conveyor device  2  and the robot  4  can be recognized with high accuracy. Since the first and second receiving device supports  15  and  16  can be omitted, this allows the robot system  1  to be a resource saving system. 
     The entire disclosure of Japanese Patent Application No. 2008-288533 filed Nov. 11, 2008 is expressly incorporated by reference herein.