Patent Publication Number: US-2021178602-A1

Title: Robot System And Control Method For Robot System

Description:
The present application is based on, and claims priority from JP Application Serial Number 2019-224689, filed Dec. 12, 2019, the disclosure of which is hereby incorporated by reference herein in its entirety. 
     BACKGROUND 
     1. Technical Field 
     The present disclosure relates to a robot system and a control method for the robot system. 
     2. Related Art 
     JP-A-2018-132829 (Patent Literature 1) discloses, as a control device that controls control targets such as machines and equipment, a programmable logic controller including a CPU unit, a power supply unit, and an IO unit. The CPU unit includes a microprocessor, a memory, a chip set, and a communication controller including a system timer. The system timer generates an interrupt signal at every fixed time interval and provides the interrupt signal to the microprocessor. The microprocessor repeatedly executes a control program at a predetermined period using the interrupt signal generated by the system timer to thereby realize operation for controlling a control target. 
     In such a CPU unit, the microprocessor and the memory are coupled via the chip set. Therefore, when a control program with a large load is executed in the microprocessor, resources such as the chip set and the memory are sometimes occupied by the control program. At this time, when another program using the interrupt signal accesses the memory via the chip set, acquisition of data from the memory is sometimes delayed. Then, timing when the other program is executed deviates from original timing. 
     For example, in a robot including a robot arm, driving of the robot arm is controlled based on position information acquired by an encoder. The robot includes a camera. A control device processes an image captured by the camera to thereby use the image for driving control for the robot arm. Therefore, the control device of the robot is considered to have the same device configuration as a device configuration of the programmable logic controller described in Patent Literature 1. 
     In the robot in which the image processing explained above is performed, while the image processing is performed in the control device, resources of the control device are occupied by the image processing. Timing for requesting position information to the encoder deviates from original timing. As a result, accurate position information cannot be acquired. Accuracy of driving speed of the robot arm is deteriorated. 
     SUMMARY 
     A robot system according to an application example of the present disclosure includes: a robot arm; encoders configured to acquire position information of the robot arm; a first control section configured to execute control processing for controlling operation of the robot arm; and a second control section provided independently from the first control section and configured to transmit a position information request signal for requesting the position information to the encoders. The second control section transmits an interrupt signal to the first control section according to the transmission of the position information request signal. The first control section executes the control processing based on the interrupt signal and the position information output from the encoders based on the position information request signal. 
     A control method for a robot system according to an application example of the present disclosure is a control method for a robot system including: a robot arm; encoders configured to acquire position information of the robot arm; a first control section configured to execute control processing for controlling operation of the robot arm; and a second control section provided independently from the first control section and configured to transmit a position information request signal for requesting the position information to the encoders. The control method includes: transmitting, with the second control section, the position information request signal to the encoders and transmitting, with the second control section, an interrupt signal corresponding to the position information request signal to the first control section; and executing the control processing based on the interrupt signal and the position information output from the encoders based on the position information request signal. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a side view showing a robot system according to a first embodiment. 
         FIG. 2  is a block diagram of the robot system shown in  FIG. 1 . 
         FIG. 3  is a diagram showing an example of processing allocated to cores shown in  FIG. 2 . 
         FIG. 4  is a timing chart in which flows of signals and data between a control device and a robot shown in  FIG. 2  are summarized along an elapsed time. 
         FIG. 5  is a timing chart in which flows of signals and data between a control device and a robot in related art are summarized along an elapsed time. 
         FIG. 6  is a schematic diagram for explaining an abnormality detecting function of a first control section. 
         FIG. 7  is a table showing an example of a first control section side axis number and an example of a second control section side axis number corresponding to an interrupt signal received by the first control section. 
     
    
    
     DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     Preferred embodiments of a robot system and a control method for the robot system according to the present disclosure are explained in detail below with reference to the accompanying drawings. 
     1. First Embodiment 
     First, a robot system according to a first embodiment is explained. 
       FIG. 1  is a side view showing the robot system according to the first embodiment.  FIG. 2  is a block diagram of the robot system shown in  FIG. 1 . 
     1.1 Overview of the Robot System 
     A robot system  1  shown in  FIG. 1  includes a robot  2  and a control device  5  that controls the operation of the robot  2 . Uses of the robot system  1  are not particularly limited. Examples of the uses of the robot system  1  include supply, removal, conveyance, and assembly of a precision instrument and components configuring the precision instrument. 
     The robot  2  shown in  FIG. 1  includes a base  21 , a robot arm  22  coupled to the base  21 , and an imaging section  4  provided in the robot arm  22 . 
     The base  21  is fixed to an installation part such as a floor, a wall, a ceiling, or a movable truck. 
     The robot arm  22  includes an arm  221  coupled to the base  21  to be capable of turning around a first axis Jl, an arm  222  coupled to the arm  221  to be capable of turning around a second axis J 2 , an arm  223  coupled to the arm  222  to be capable of turning around a third axis J 3 , an arm  224  coupled to the arm  223  to be capable of turning around a fourth axis J 4 , an arm  225  coupled to the arm  224  to be capable of turning around a fifth axis J 5 , and an arm  226  coupled to the arm  225  to be capable of turning around a sixth axis J 6 . An end effector  26  corresponding to work to be executed by the robot  2  is attached to the arm  226 . 
     The configuration of the robot  2  is not limited to the configuration in this embodiment. For example, the number of arms of the robot arm  22  may be one to five or may be seven or more. A type of the robot  2  may be a SCARA robot or a double-arm robot including two robot arms  22 . 
     The robot  2  includes, as shown in  FIG. 2 , a first driving section  231 , a second driving section  232 , a third driving section  233 , a fourth driving section  234 , a fifth driving section  235 , and a sixth driving section  236 . The first driving section  231  includes a not-shown motor that turns the arm  221  with respect to the base  21  and a not-shown speed reducer. The second driving section  232  includes a not-shown motor that turns the arm  222  with respect to the arm  221  and a not-shown speed reducer. The third driving section  233  includes a not-shown motor that turns the arm  223  with respect to the arm  222  and a not-shown speed reducer. The fourth driving section  234  includes a not-shown motor that turns the arm  224  with respect to the arm  223  and a not-shown speed reducer. The fifth driving section  235  includes a not-shown motor that turns the arm  225  with respect to the arm  224  and a not-shown speed reducer. The sixth driving section  236  includes a not-shown motor that turns the arm  226  with respect to the arm  225  and a not-shown speed reducer. 
     The control device  5  controls the operations of the first driving section  231 , the second driving section  232 , the third driving section  233 , the fourth driving section  234 , the fifth driving section  235 , and the sixth driving section  236  to move the arms  221  to  226  to target positions. 
     The robot  2  includes encoders  24  that are provided in rotating shafts of the motors or the speed reducers of the driving sections and detect rotation angles of the rotating shafts. The encoders  24  acquire position information of the robot arm  22 . The position information means information indicating rotation angles of the rotating shafts. The encoders  24  have a function of transmitting the acquired position information to the control device  5  for each of the rotating shafts. 
     In the robot  2  according to this embodiment, the encoders  24  are multiplexed. The multiplexing means making it possible to acquire a plurality of kinds of position information by providing a plurality of encoders for each of the rotating shafts. Therefore, it is possible to impart redundancy to the encoders  24  and more highly accurately detect the positions and the speeds of the rotating shafts. 
     Specifically, the encoders  24  include a first main encoder  241   a,  a first sub-encoder  241   b,  a second main encoder  242   a,  a second sub-encoder  242   b,  a third main encoder  243   a,  a third sub-encoder  243   b,  a fourth main encoder  244   a,  a fourth sub-encoder  244   b,  a fifth main encoder  245   a,  a fifth sub-encoder  245   b,  a sixth main encoder  246   a,  and a sixth sub-encoder  246   b.    
     The first main encoder  241   a  and the first sub-encoder  241   b  that detect a rotation angle of the rotating shaft of the motor or the speed reducer of the first driving section  231  are provided in the motor or the speed reducer. The second main encoder  242   a  and the second sub-encoder  242   b  that detect a rotation angle of the rotating shaft of the motor or the speed reducer of the second driving section  232  are provided in the motor or the speed reducer. The third main encoder  243   a  and the third sub-encoder  243   b  that detect a rotation angle of the rotating shaft of the motor or the speed reducer of the third driving section  233  are provided in the motor or the speed reducer. The fourth main encoder  244   a  and the fourth sub-encoder  244   b  that detect a rotation angle of the rotating shaft of the motor or the speed reducer of the fourth driving section  234  are provided in the motor or the speed reducer. The fifth main encoder  245   a  and the fifth sub-encoder  245   b  that detect a rotation angle of the rotating shaft of the motor or the speed reducer of the fifth driving section  235  are provided in the motor or the speed reducer. The sixth main encoder  246   a  and the sixth sub-encoder  246   b  that detect a rotation angle of the rotating shaft of the motor or the speed reducer of the sixth driving section  236  are provided in the motor or the speed reducer. 
     Examples of the motors include an AC servomotor and a DC servomotor. Examples of the speed reducers include a planetary gear-type speed reducer and a wave gear device. 
     The motors are electrically coupled to the control device  5  via not-shown motor drivers. The encoders  24  are also electrically coupled to the control device  5 . 
     The imaging section  4  is attached to the robot arm  22  and images a target of work by the robot  2  and the end effector  26 . The imaging section  4  is electrically coupled to the control device  5 . 
     1.2. Hardware Configuration of the Control Device 
     The control device  5  is communicably coupled to the robot  2 . The control device  5  and the robot  2  may be coupled by wire or may be coupled by radio. 
     The control device  5  includes a first control section  51 , a second control section  52 , a system bus  53 , and a main memory  54 . 
     The first control section  51  includes a processor such as a CPU (Central Processing Unit) or an MPU (Micro Processing Unit). The processor may be a single-core processor that operates in a multi-task manner. However, the processor is preferably a multi-core processor. By using the multi-core processor, execution of different application programs can be allocated to cores. Consequently, it is possible to smoothly execute the application programs and improve performance, in particular, real-time properties of the control device  5 . 
     The first control section  51  shown in  FIG. 2  includes a multi-core processor. The processor includes a first core  511 , a second core  512 , a third core  513 , and a fourth core  514 . The number of cores of the processor is not limited to four. 
       FIG. 3  is a diagram showing an example of processing allocated to the cores shown in  FIG. 2 . The example shown in  FIG. 3  is an example in which the multi-core processor used in the first control section  51  is operated by asymmetrical multiprocessing (AMP). The asymmetrical multiprocessing is a technique for mixing different OSs (Operating Systems) and bear metals on one processor. 
     Control processing for the robot  2  including robot arm control processing for controlling the operation of the robot arm  22  is allocated to the first core  511 . 
     Image processing is allocated to the second core  512  and the third core  513 . Examples of the image processing include imaging processing by the imaging section  4  and filter processing for an obtained image. 
     A general-purpose OS such as Linux (registered trademark) is allocated to the first core  511 , the second core  512 , and the third corer  513 . Consequently, it is possible to cause the first core  511 , the second core  512 , and the third core  513  to execute various kinds of general-purpose processing including the processing described above. Examples of the general-purpose processing include, besides the image processing, arithmetic operation processing for outputs of a force sensor, a pressure sensor, and a proximity sensor. 
     For example, processing concerning an operation position of the robot arm  22 , processing concerning operating speed of the robot arm  22 , processing concerning communication with the second control section  52 , and processing concerning other communication are allocated to the fourth core  514 . These kinds of processing are respectively processing requested to be executed at a predetermined time interval. Therefore, the processing is referred to as “predetermined interval processing” herein. Examples of the other communication include processing concerning a field bus and processing concerning a standard input and output. The predetermined time interval is not particularly limited but is set to, for example, several ten microseconds to several milliseconds. 
     The fourth core  514  is a so-called bear metal to which, for example, an OS is not allocated. The bear metal is also called bear metal-type hypervisor and means a virtual environment that makes it possible to directly execute an application program on hardware not via an OS or virtual software for constructing the virtual environment. By forming the fourth core  514  as the bear metal, it is easier to execute the predetermined interval processing without delay compared with when the general-purpose OS is allocated to the fourth core  514 . That is, it is possible to improve the real-time properties. The fourth core  514  is not limited to the bear metal. For example, any OS may be allocated to the fourth core  514 . 
     The first control section  51  may include not-shown primary cache memories respectively corresponding to the first core  511 , the second core  512 , the third core  513 , and the fourth core  514 . 
     On the other hand, the first control section  51  shown in  FIG. 2  includes a secondary cache memory  515  common to the first core  511 , the second core  512 , the third core  513 , and the fourth core  514 . 
     The cores and the cores and the secondary cache memory  515  are communicably coupled via not-shown interconnects. 
     The first control section  51  may include a not-shown system timer and the like besides the cache memories. 
     A hardware configuration of the first control section  51  may be a configuration in which the sections explained above are physically independent from one another but is preferably a configuration in which the sections are integrated in one chip. Specifically, the hardware configuration of the first control section  51  is preferably an SoC (System On Chip). Consequently, it is possible to realize a reduction in the size, power saving, and a reduction in the cost of the first control section  51 . 
     The second control section  52  includes elements such as an FPGA (Field-Programmable Gate Array) and an ASIC (Application Specific Integrated Circuit). The second control section  52  has a function of generating a timing signal at a predetermined time interval, a function of generating an interrupt signal simultaneously with the timing signal generation and transmitting the interrupt signal to the first control section  51 , and a function of generating a position information request signal simultaneously with the timing signal generation and transmitting the position information request signal to the encoders  24 . 
     The second control section  52  is communicably coupled to the first control section  51  via the system bus  53  shown in  FIG. 2 . 
     The main memory  54  is communicably coupled to the system bus  53 . Examples of the main memory  54  include a RAM (Random Access Memory). Besides, not-shown various interfaces, a not-shown nonvolatile memory, a not-shown communication controller, and the like may be communicably coupled to the system bus  53 . The system bus  53  may be independently configured as a first dedicated bus that couples the first control section  51  and the second control section  52  and a second dedicated bus that couples the first control section  51  and the main memory  54 . 
     1.3. Software Configuration of the Control Device 
     A software configuration of the control device  5 , that is, an operation example of the control device  5  is explained. In the following explanation, signals and data transmitted and received between the control device  5  and the robot  2  are explained taking, as an example, a process in which the control device  5  acquires position information and speed information from the encoders  24 . 
       FIG. 4  is a timing chart in which flows of signals and data between the control device  5  and the robot  2  shown in  FIG. 2  are summarized along an elapsed time. In  FIG. 4 , arrows indicate the flows of the signals and the data. Solid line squares indicate processing, operations, or transmission and reception of signals. The arrows connect the solid line squares. 
     The horizontal axis of  FIG. 4  is a time axis. Time flows from the left to the right. In  FIG. 4 , a first period is represented as a period t 1  and the next period is represented as a period t 2 . A period t 3 , a period t 4 , . . . follow thereafter. The lengths of the periods are equal to one another. A processing target axis shown in  FIG. 4  indicates a target axis of processing concerning position information executed in a time division manner by the fourth core  514  of the first control section  51 . Specifically, the processing target axis indicates which of the first axis J 1 , the second axis J 2 , the third axis J 3 , the fourth axis J 4 , the fifth axis J 5 , and the sixth axis J 6  the target axis of the processing of the position information by the fourth core  514  of the first control section  51  is in the periods. The first to sixth axes J 1  to J 6  are set in order as the processing target axis. The setting of the first to sixth axes J 1  to J 6  is repeated. 
     The sections of the control device  5  or the robot  2  are enumerated on the vertical axis of  FIG. 4 . Start points and end points of the arrows are respectively located in any one of the sections shown on the vertical axis of  FIG. 4 . A transmission side of the second control section  52  shown in  FIG. 4  indicates, in the second control section  52 , regions for transmitting signals to the sections. A reception side of the second control section  52  shown in  FIG. 4  indicates, in the second control section  52 , regions for receiving data of position information from the encoders  24  and transmitting the data to the first control section  51 . 
     1.3.1. Period t 1   
     In the first period t 1  shown in  FIG. 4 , an interrupt signal si 4  is transmitted from the second control section  52  to the first control section  51  based on one timing signal st 4  generated by the second control section  52 . 
     The fourth core  514  of the first control section  51  receives the interrupt signal si 4  and executes, with the reception of the interrupt signal si 4  as a trigger, processing concerning the position of the fourth axis J 4 . This processing includes acquisition processing pg 4  for acquiring not-shown position information concerning the fourth axis J 4  transmitted from the second control section  52  in a period before the period t 1  and arithmetic operation processing pc 4  for calculating a position and speed of the fourth axis J 4  from the position information. The position of the fourth axis J 4 , that is, a turning angle from the origin of the fourth axis J 4  is obtained by these kinds of processing. Turning speed of the fourth axis J 4  is obtained based on an amount of change per unit time of the calculated position. Details of the processing are explained below. 
     On the other hand, in the period t 1 , a position information request signal sr 1  is transmitted from the second control section  52  to the first main encoder  241   a  and the first sub-encoder  241   b  based on one timing signal st 4  generated by the second control section  52 . 
     The first main encoder  241   a  and the first sub-encoder  241   b  respectively receive the position information request signal sr 1  and perform, with the reception of the position information request signal sr 1  as a trigger, a position detecting operation pr 1  for detecting the position of the first axis J 1 . Subsequently, the first main encoder  241   a  and the first sub-encoder  241   b  transmit, in order, to the second control section  52 , first main position information dm 1  and first sub-position information ds 1 , which are information concerning the position of the first axis J 1  acquired by the position detecting operation pr 1 . 
     The second control section  52  receives the first main position information dm 1  and the first sub-position information ds 1  and integrates these kinds of information. The second control section  52  saves the integrated information in, for example, the secondary cache memory  515  as first position information d 1  concerning the position and the status of the first axis J 1 . The first control section  51  reads out the first position information d 1 . 
     The transmission and reception of the various signals and the data do not need to be performed in the period t 1  and may be performed in a period after the period t 1 . In  FIG. 4 , as an example, the transmission of the first main position information dm 1  and the first sub-position information ds 1  and the readout of the first position information d 1  are respectively performed in the period t 2 . 
     The first position information d 1  may be saved in the secondary cache memory  515  or may be saved in a not-shown storing section included in the second control section  52 . The same applies to second position information d 2  and subsequent position information explained below. 
     1.3.2. Period t 2   
     In the period t 2  shown in  FIG. 4 , an interrupt signal si 5  is transmitted from the second control section  52  to the first control section  51  based on a timing signal sty generated by the second control section  52 . 
     The fourth core  514  of the first control section  51  receives the interrupt signal si 5  and executes, with the reception of the interrupt signal si 5  as a trigger, processing concerning the position of the fifth axis J 5 . This processing includes acquisition processing pg 5  for acquiring not-shown position information concerning the fifth axis J 5  transmitted from the second control section  52  in a period before the period t 2  and arithmetic operation processing pc 5  for calculating a position and speed of the fifth axis J 5  from the position information. The position of the fifth axis J 5 , that is, a turning angle from the origin of the fifth axis J 5  is obtained by these kinds of processing. Turning speed of the fifth axis J 5  is obtained based on an amount of change per unit time of the calculated position. Details of the processing are explained below. 
     On the other hand, in the period t 2 , a position information request signal sr 2  is transmitted from the second control section  52  to the second main encoder  242   a  and the second sub-encoder  242   b  based on the timing signal sty generated by the second control section  52 . 
     The second main encoder  242   a  and the second sub-encoder  242   b  respectively receive the position information request signal sr 2  and perform, with the reception of the position information request signal sr 2  as a trigger, a position detecting operation pr 2  for detecting the position of the second axis J 2 . Subsequently, the second main encoder  242   a  and the second sub-encoder  242   b  transmit, in order, to the second control section  52 , second main position information dm 2  and second sub-position information ds 2 , which are information concerning the position of the second axis J 2  acquired by the position detecting operation pr 2 . 
     The second control section  52  receives the second main position information dm 2  and the second sub-position information ds 2  and integrates these kinds of information. The second control section  52  saves the integrated information in, for example, the secondary cache memory  515  as second position information d 2  concerning the position and the status of the second axis J 2 . The first control section  51  reads out the second position information d 2 . 
     The transmission and reception of the various signals and the data do not need to be performed in the period t 2  and may be performed in a period after the period t 2 . In  FIG. 4 , as an example, the transmission of the second main position information dm 2  and the second sub-position information ds 2  and the readout of the second position information d 2  are respectively performed in the period t 3 . 
     1.3.3. Period t 3   
     In the period t 3  shown in  FIG. 4 , an interrupt signal si 6  is transmitted from the second control section  52  to the first control section  51  based on a timing signal st 6  generated by the second control section  52 . 
     The fourth core  514  of the first control section  51  receives the interrupt signal si 6  and executes, with the reception of the interrupt signal si 6  as a trigger, processing concerning the position of the sixth axis J 6 . This processing includes acquisition processing pg 6  for acquiring not-shown position information concerning the sixth axis J 6  transmitted from the second control section  52  in a period before the period t 3  and arithmetic operation processing pc 6  for calculating a position and speed of the sixth axis J 6  from the position information. The position of the sixth axis J 6 , that is, a turning angle from the origin of the sixth axis J 6  is obtained by these kinds of processing. Turning speed of the sixth axis J 6  is obtained based on an amount of change per unit time of the calculated position. Details of the processing are explained below. 
     On the other hand, in the period t 3 , a position information request signal sr 3  is transmitted from the second control section  52  to the third main encoder  243   a  and the third sub-encoder  243   b  based on the timing signal st 6  generated by the second control section  52 . 
     The third main encoder  243   a  and the third sub-encoder  243   b  respectively receive the position information request signal sr 3  and perform, with the reception of the position information request signal sr 3  as a trigger, a position detecting operation pr 3  for detecting the position of the third axis J 3 . Subsequently, the third main encoder  243   a  and the third sub-encoder  243   b  transmit, in order, to the second control section  52 , third main position information dm 3  and third sub-position information ds 3 , which are information concerning the position of the third axis J 3  acquired by the position detecting operation pr 3 . 
     The second control section  52  receives the third main position information dm 3  and the third sub-position information ds 3  and integrates these kinds of information. The second control section  52  saves the integrated information in, for example, the secondary cache memory  515  as third position information d 3  concerning the position and the status of the third axis J 3 . The first control section  51  reads out the third position information d 3 . 
     The transmission and reception of the various signals and the data do not need to be performed in the period t 3  and may be performed in a period after the period t 3 . In  FIG. 4 , as an example, the transmission of the third main position information dm 3  and the third sub-position information ds 3  and the readout of the third position information d 3  are respectively performed in the period t 4 . 
     1.3.4. Period t 4   
     In the period t 4  shown in  FIG. 4 , an interrupt signal si 1  is transmitted from the second control section  52  to the first control section  51  based on a timing signal stl generated by the second control section  52 . 
     The fourth core  514  of the first control section  51  receives the interrupt signal si 1  and executes, with the reception of the interrupt signal si 1  as a trigger, processing concerning the position of the first axis J 1 . 
     This processing includes acquisition processing pg 1  for acquiring the first position information d 1  concerning the first axis J 1  transmitted from the second control section  52  in the period t 1  and arithmetic operation processing pc 1  for calculating a position and speed of the first axis J 1  from the position information. The position of the first axis J 1 , that is, a turning angle from the origin of the first axis J 1  is obtained by these kinds of processing. Turning speed of the first axis J 1  is obtained based on an amount of change per unit time of the calculated position. 
     In the fourth core  514 , when the acquisition processing pg 1  and the arithmetic operation processing pc 1  are executed, timing for the execution is determined based on the interrupt signal si 1  as explained above. Timing when the first position information d 1  used for these kinds of processing is transmitted to the first control section  51  is determined based on the position information request signal sr 1  transmitted from the second control section  52  in the period t 1  explained above. 
     Therefore, the interrupt signal si 1  is transmitted based on the timing signal st 1 . The position information request signal sr 1  is transmitted based on the timing signal st 4  in the period t 1 . The timing signals st 1  and st 4  are accurately generated at a predetermined interval in the second control section  52  independent from the first control section  51 . Consequently, the first position information d 1  saved in the secondary cache memory  515  according to the position information request signal sr 1  can be read out by the first control section  51  in the period t 4 . In other words, by optimizing transmission timings of the signals using the highly accurate timing signals st 1  and st 4 , immediately before starting the acquisition processing pg 1  and the arithmetic operation processing pc 1 , the first control section  51  is capable of reading the first position information d 1  necessary for the processing. Consequently, it is unnecessary to separately prepare processing for synchronizing timings of the processing. It is possible to achieve simplification of the configuration of the control device  5 . 
     On the other hand, in the period t 4 , a position information request signal sr 4  is transmitted from the second control section  52  to the fourth main encoder  244   a  and the fourth sub-encoder  244   b  based on the timing signal stl generated by the second control section  52 . 
     The fourth main encoder  244   a  and the fourth sub-encoder  244   b  respectively receive the position information request signal sr 4  and perform, with the reception of the position information request signal sr 4  as a trigger, a position detecting operation pr 4  for detecting the position of the fourth axis J 4 . Subsequently, the fourth main encoder  244   a  and the fourth sub-encoder  244   b  transmit, in order, to the second control section  52 , fourth main position information dm 4  and fourth sub-position information ds 4 , which are information concerning the position of the fourth axis J 4  acquired by the position detecting operation pr 4 . 
     The second control section  52  receives the fourth main position information dm 4  and the fourth sub-position information ds 4  and integrates these kinds of information. The second control section  52  saves the integrated information in, for example, the secondary cache memory  515  as fourth position information d 4  concerning the position and the status of the fourth axis J 4 . The first control section  51  reads out the fourth position information d 4 . 
     The transmission and reception of the various signals and the data do not need to be performed in the period t 4  and may be performed in a period after the period t 4 . In  FIG. 4 , as an example, the transmission of the fourth main position information dm 4  and the fourth sub-position information ds 4  and the readout of the fourth position information d 4  are respectively performed in the period t 5 . 
     1.3.5. Period t 5   
     In the period t 5  shown in  FIG. 4 , an interrupt signal si 2  is transmitted from the second control section  52  to the first control section  51  based on a timing signal st 2  generated by the second control section  52 . 
     The fourth core  514  of the first control section  51  receives the interrupt signal si 2  and executes, with the reception of the interrupt signal si 2  as a trigger, processing concerning the position of the second axis J 2 . This processing includes acquisition processing pg 2  for acquiring the second position information d 2  concerning the second axis J 2  transmitted from the second control section  52  in the period t 2  and arithmetic operation processing pc 2  for calculating a position and speed of the second axis J 2  from the position information. The position of the second axis J 2 , that is, a turning angle from the origin of the second axis J 2  is obtained by these kinds of processing. Turning speed of the second axis J 2  is obtained based on an amount of change per unit time of the calculated position. 
     In the fourth core  514 , when the acquisition processing pg 2  and the arithmetic operation processing pc 2  are executed, timing for the execution is determined based on the interrupt signal si 2  as explained above. Timing when the second position information d 2  used for these kinds of processing is transmitted to the first control section  51  is determined based on the position information request signal sr 2  transmitted from the second control section  52  in the period t 2  explained above. 
     Therefore, the interrupt signal si 2  is transmitted based on the timing signal st 2 . The position information request signal sr 2  is transmitted based on the timing signal st 5  in the period t 2 . The timing signals st 2  and st 5  are accurately generated at a predetermined interval in the second control section  52  independent from the first control section  51 . Consequently, the second position information d 2  saved in the secondary cache memory  515  according to the position information request signal sr 2  can be read out by the first control section  51  in the period t 5 . In other words, by optimizing transmission timings of the signals using the highly accurate timing signals st 2  and st 5 , immediately before starting the acquisition processing pg 2  and the arithmetic operation processing pc 2 , the first control section  51  is capable of reading the second position information d 2  necessary for the processing. Consequently, it is unnecessary to separately prepare processing for synchronizing both timings of the processing. It is possible to achieve simplification of the configuration of the control device  5 . 
     On the other hand, in the period t 5 , a position information request signal sr 5  is transmitted from the second control section  52  to the fifth main encoder  245   a  and the fifth sub-encoder  245   b  based on the timing signal st 2  generated by the second control section  52 . 
     The fifth main encoder  245   a  and the fifth sub-encoder  245   b  respectively receive the position information request signal sr 5  and perform, with the reception of the position information request signal sr 5  as a trigger, a position detecting operation pr 5  for detecting the position of the fifth axis J 5 . Subsequently, the fifth main encoder  245   a  and the fifth sub-encoder  245   b  transmit, in order, to the second control section  52 , fifth main position information dm 5  and fifth sub-position information ds 5 , which are information concerning the position of the fifth axis J 5  acquired by the position detecting operation pr 5 . 
     The second control section  52  receives the fifth main position information dm 5  and the fifth sub-position information ds 5  and integrates these kinds of information. The second control section  52  saves the integrated information in, for example, the secondary cache memory  515  as fifth position information d 5  concerning the position and the status of the fifth axis J 5 . The first control section  51  reads out the fifth position information d 5 . 
     The transmission and reception of the various signals and the data do not need to be performed in the period t 5  and may be performed in a period after the period t 5 . In  FIG. 4 , as an example, the transmission of the fifth main position information dm 5  and the fifth sub-position information ds 5  and the readout of the fifth position information d 5  are respectively performed in the period t 6 . 
     1.3.6. Period t 6   
     In the period t 6  shown in  FIG. 4 , an interrupt signal si 3  is transmitted from the second control section  52  to the first control section  51  based on a timing signal st 3  generated by the second control section  52 . 
     The fourth core  514  of the first control section  51  receives the interrupt signal si 3  and executes, with the reception of the interrupt signal si 3  as a trigger, processing concerning the position of the third axis J 3 . This processing includes acquisition processing pg 3  for acquiring the third position information d 3  concerning the third axis J 3  transmitted from the second control section  52  in the period t 3  and arithmetic operation processing pc 3  for calculating a position and speed of the third axis J 3  from the position information. The position of the third axis J 3 , that is, a turning angle from the origin of the third axis J 3  is obtained by these kinds of processing. Turning speed of the third axis J 3  is obtained based on an amount of change per unit time of the calculated position. 
     In the fourth core  514 , when the acquisition processing pg 3  and the arithmetic operation processing pc 3  are executed, timing for the execution is determined based on the interrupt signal si 3  as explained above. On the other hand, timing when the third position information d 3  used for these kinds of processing is transmitted to the first control section  51  is determined based on the position information request signal sr 3  transmitted from the second control section  52  in the period t 3  explained above. 
     Therefore, the interrupt signal si 3  is transmitted based on the timing signal st 3 . The position information request signal sr 3  is transmitted based on the timing signal st 6  in the period t 3 . The timing signals st 3  and st 6  are accurately generated at a predetermined interval in the second control section  52  independent from the first control section  51 . Consequently, the third position information d 3  saved in the secondary cache memory  515  according to the position information request signal sr 3  can be read out by the first control section  51  in the period t 6 . In other words, by optimizing transmission timings of the signals using the highly accurate timing signals st 3  and st 6 , immediately before starting the acquisition processing pg 3  and the arithmetic operation processing pc 3 , the first control section  51  is capable of reading the third position information d 3  necessary for the processing. Consequently, it is unnecessary to separately prepare processing for synchronizing both timings of the processing. It is possible to achieve simplification of the configuration of the control device  5 . 
     On the other hand, in the period t 6 , a position information request signal sr 6  is transmitted from the second control section  52  to the sixth main encoder  246 a and the sixth sub-encoder  246   b  based on the timing signal st 3  generated by the second control section  52 . 
     The sixth main encoder  246   a  and the sixth sub-encoder  246   b  respectively receive the position information request signal sr 6  and perform, with the reception of the position information request signal sr 6  as a trigger, a position detecting operation pr 6  for detecting the position of the sixth axis J 6 . Subsequently, the sixth main encoder  246   a  and the sixth sub-encoder  246   b  transmit, in order, to the second control section  52 , sixth main position information dm 6  and sixth sub-position information ds 6 , which are information concerning the position of the sixth axis J 6  acquired by the position detecting operation pr 6 . 
     The second control section  52  receives the sixth main position information dm 6  and the sixth sub-position information ds 6  and integrates these kinds of information. The second control section  52  saves the integrated information in, for example, the secondary cache memory  515  as sixth position information d 6  concerning the position and the status of the sixth axis J 6 . The first control section  51  reads out the sixth position information d 6 . 
     The transmission and reception of the various signals and the data do not need to be performed in the period t 6  and may be performed in a period after the period t 6 . In  FIG. 4 , as an example, the transmission of the sixth main position information dm 6  and the sixth sub-position information ds 6  and the readout of the sixth position information d 6  are respectively performed in a period t 7 . 
     1.3.7. Period t 7  and Subsequent Periods 
     In the period t 7  and subsequent periods shown in  FIG. 4 , specifically, in periods t 7  to t 10 , transmission and reception of signals and data, operations, processing, and the like are repeated as in the periods t 1  to t 6  explained above. As a result, the control device  5  can acquire positions, speeds, and the like of the first to sixth axes J 1  to J 6  at a predetermined interval. The control device  5  is capable of appropriately controlling the operation of the robot arm  22  based on the acquired position, speed, and the like. 
     1.3.8. Comparison With Related Art 
     Differences between related art and this embodiment are explained. 
       FIG. 5  is a timing chart in which flows of signals and data between a control device and a robot in related art are summarized along an elapsed time. The horizontal axis and the vertical axis of  FIG. 5  are the same as the horizontal axis and the vertical axis of  FIG. 4 . For convenience of explanation, the same components as the components shown in  FIG. 4  are denoted by the same reference numerals and signs. 
     In  FIG. 4  referred to above, the position information request signals sr 1 , sr 2 , sr 3 , sr 4 , . . . are transmitted from the second control section  52  based on the timing signals st 4 , st 5 , st 6 , st 1 , . . . generated by the second control section  52 . A generation period of the timing signals st 4 , st 5 , st 6 , st 1 , . . . is not particularly limited. For example, the generation period is several ten microseconds. 
     On the other hand, in  FIG. 5  showing related art, control signals sc 4 ′, sc 5 ′, sc 6 ′, sc 1 ′, concerning acquisition of position information are transmitted from the first control section  51  instead of these timing signals. The second control section  52 , which receives the control signals, transmits position information request signals sr 1 ′, sr 2 ′, sr 3 ′, sr 4 ′, . . . to the encoders  24 . 
     That is, in  FIG. 4  referred to above, the timing signals st 4 , sty, st 6 , st 1 , . . . are generated from the second control section  52 . The position information request signals sr 1 , sr 2 , sr 3 , sr 4 , . . . are transmitted from the second control section  52  based on the timing signals. On the other hand, in  FIG. 5  showing related art, the control signals sc 4 ′, sc 5 ′, sc 6 ′, sc 1 ′, . . . are transmitted from the first control section  51  to the second control section  52 . The position information request signals sr 1 ′, sr 2 ′, sr 3 ′, sr 4 ′, . . . are transmitted from the second control section  52  based on the control signals. 
     In this case, a transmission interval of the position information request signals sr 1 ′, sr 2 ′, sr 3 ′, sr 4 ′, . . . depends on a transmission interval of the control signals sc 4 ′, sc 5 ′, sc 6 ′, sc 1 ′, . . . . 
     Transmission of the control signals sc 4 ′, sc 5 ′, sc 6 ′, sc 1 ′, . . . in the first control section  51  is performed based on the predetermined interval processing in the fourth core  514 . It is assumed that the predetermined interval processing for transmitting the control signals sc 4 ′, sc 5 ′, sc 6 ′, sc 1 ′, . . . is executed immediately before the acquisition processing pg 4 , pg 5 , pg 6 , pg 1 , . . . . 
     However, in the first control section  51 , general-purpose processing such as image processing is sometimes executed in parallel to the predetermined interval processing. Such general-purpose processing temporarily occupies the secondary cache memory  515  and the system bus  53  of the first control section  51 . Then, a program necessary for the predetermined interval processing is evicted from the secondary cache memory  515 . A delay occurs in timing for starting the predetermined interval processing. This is a problem in related art. This problem is more specifically explained below. 
     In  FIG. 5  showing related art, an example is shown in which a start of the predetermined interval processing for transmitting the control signal sc 4 ′ is delayed in the period t 7 . When the transmission of the control signal sc 4 ′ is delayed, timing for transmitting the position information request signal sr 1 ′ from the second control section  52  is also delayed. Then, a start of the position detecting operation pr 1  for detecting the position of the first axis J 1  is also delayed. Transmission of the first main position information dm 1  and the first sub-position information ds 1  and transmission of the first position information d 1  are respectively also delayed. In  FIG. 5 , for convenience of explanation, the predetermined interval processing in the period t 7 , the start of which is delayed, is indicated by dots. Processing and operation affected by the delay are also indicated by dots. 
     On the other hand, an example is shown in which, in the period t 8  in  FIG. 5 , the predetermined interval processing for transmitting the control signal sc 5 ′ is started at timing assumed in the beginning. Then, timing for transmitting the position information request signal sr 2 ′ from the second control section  52  is also as assumed. Timing for starting the position detecting operation pr 2  for detecting the position of the second axis J 2  is also as assumed. Transmission of the second main position information dm 2  and the second sub-position information ds 2  and transmission of the second position information d 2  are also performed at timing as assumed in the beginning. 
     As a result of the above, in the second control section  52 , as shown in  FIG. 5 , for example, a period in which the first sub-position information ds 1  is received and a period in which the second main position information dm 2  is received overlap. Consequently, crosstalk of data occurs in the second control section  52 . Normal data cannot be obtained. As a result, accurate positions and speeds cannot be acquired about the first axis J 1  and the second axis J 2 . 
     The first control section  51  calculates speeds from the positions of the axes based on the premise that the position detecting operations pr 1 , pr 2 , pr 3 , pr 4 , . . . are executed at a predetermined time interval. However, as shown in  FIG. 5 , when the transmission of the control signal sc 4 ′ is delayed, a start of the position detecting operation pr 1  is delayed. This premise is broken. Consequently, accuracy of calculated speed is also deteriorated. 
     On the other hand, in  FIG. 4  showing this embodiment, the position information request signals sr 1 , sr 2 , sr 3 , sr 4 , . . . are transmitted from the second control section  52  based on the timing signals st 4 , st 5 , st 6 , st 1 , . . . generated by the second control section  52 . The timing signals st 4 , st 5 , st 6 , and st 1 , . . . are signals generated from the second control section  52  independent from the first control section  51 . Therefore, a generation interval of the timing signals st 4 , st 5 , st 6 , st 1 , . . . is maintained at a predetermined interval irrespective of a state of the first control section  51 . That is, in the first control section  51 , even when the secondary cache memory  515  and the system bus  53  are occupied by image processing or the like, the generation interval of the timing signals st 4 , st 5 , st 6 , st 1 , . . . is not affected by the occupation. Therefore, the transmission of the position information request signals sr 1 , sr 2 , sr 3 , sr 4 , . . . transmitted based on the timing signals st 4 , st 5 , st 6 , st 1 , . . . is not delayed irrespective of the state of the first control section  51 . As a result, occurrence of crosstalk of data is prevented and the premise is maintained. Therefore, the control device  5  can acquire accurate positions and speeds. 
     However, in this embodiment as well, a delay of the predetermined interval processing could occur when the secondary cache memory  515  of the first control section  51  and the system bus  53  are occupied by the general-purpose processing. In  FIG. 4 , an example is shown in which starts of the acquisition processing pg 4  and the arithmetic operation processing pc 4  are delayed in the period t 7 . In  FIG. 4 , for convenience of explanation, processing, the starts of which are delayed, is indicated by dots. 
     However, in this embodiment, even if such a delay of the predetermined interval processing occurs, the transmission of the position information request signal sr 1  is not delayed. Accordingly, crosstalk of data is not caused. In the period t 10 , the first control section  51  can acquire normal first position information d 1 . Since the transmission of the position information request signal sr 1  is not delayed, acquisition of normal speed is guaranteed in the control device  5 . 
     The control device  5  can execute control processing for accurately controlling the operation of the robot arm  22  based on the positions and the speeds of the axes acquired in this way. 
     As explained above, the robot system  1  according to this embodiment includes the robot arm  22 , the encoders  24  that acquire position information of the robot arm  22 , the first control section  51  that executes control processing for controlling the operation of the robot arm  22 , and the second control section  52  that is provided independently from the first control section  51  and transmits the position information request signals sr 1 , sr 2 , sr 3 , sr 4 , . . . for requesting position information to the encoders  24 . The second control section  52  transmits the interrupt signal si 4 , si 5 , si 6 , si 1 , . . . to the first control section  51  according to the transmission of the position information request signals sr 1 , sr 2 , sr 3 , sr 4 , . . . . The first control section  51  executes the control processing based on the interrupt signals si 4 , si 5 , si 6 , si 1 , . . . and the position information output from the encoders  24  based on the position information request signals sr 1 , sr 2 , sr 3 , sr 4 , . . . . 
     With such a robot system  1 , the control device  5  can acquire an accurate position and accurate speed of the robot arm  22 . Accordingly, the control device  5  can accurately control the operation of the robot arm  22 . That is, in controlling the operation of the robot arm  22  based on the position information acquired from the encoders  24 , even when general-purpose processing with a large load such as image processing is executed in the first control section  51 , it is possible to realize the robot system  1  capable of suppressing deterioration in operation accuracy. 
     The second control section  52  being independent from the first control section  51  indicates a state in which the first control section  51  and the second control section  52  do not share a cache memory or a memory replacing the cache memory. Therefore, the first control section  51  and the second control section  52  may be elements separate from each other or may be integrated in one chip. 
     The robot system  1  shown in  FIG. 2  includes the imaging section  4 . The first control section  51  is configured to execute image processing for an image acquired by the imaging section  4 . Such image processing is processing that occupies the secondary cache memory  515  and the system bus  53  at a high occupancy ratio. The effects explained above are particularly significant in the control device  5  in which such processing is executed. 
     The encoders  24  shown in  FIG. 2  are multiplexed as explained above. Consequently, it is possible to impart redundancy to the encoders  24  and highly accurately detect the positions and the speeds of the rotating shafts obtained based on the position information acquired from the encoders  24 . 
     As explained above, the second control section  52  is configured to repeat the transmission of the position information request signals sr 1 , sr 2 , sr 3 , sr 4 , . . . at the predetermined interval. If the predetermined interval is known in advance, it is possible to calculate turning speeds of the axes in the first control section  51  based on the position information acquired from the encoders  24 . That is, since the turning speeds can be calculated even if time information is not included in the position information, it is possible to achieve simplification of the configuration of the control device  5 . 
     A control method for the robot system  1  according to this embodiment is a method of controlling the robot system  1  including the robot arm  22 , the encoders  24  that acquire position information of the robot arm  22 , the first control section  51  that executes control processing for controlling the operation of the robot arm  22 , and the second control section  52  that is provided independently from the first control section  51  and transmits the position information request signals sr 1 , sr 2 , sr 3 , sr 4 , . . . for requesting position information to the encoders  24 . 
     The control method includes a step of transmitting, with the second control section  52 , the position information request signals sr 1 , sr 2 , sr 3 , sr 4 , . . . to the encoders  24  and transmitting, with the second control section  52 , the interrupt signals si 4 , si 5 , si 6 , si 1 , . . . corresponding to the position information request signals sr 1 , sr 2 , sr 3 , sr 4 , . . . to the first control section  51  and a step of executing, with the first control section  51 , control processing based on the interrupt signals si 4 , si 5 , si 6 , si 1 , . . . and position information output from the encoders  24  based on the position information request signals sr 1 , sr 2 , sr 3 , sr 4 , . . . . 
     With such a control method, the control device  5  of the robot system  1  can acquire an accurate position and accurate speed of the robot arm  22 . Accordingly, the control device  5  can accurately control the operation of the robot arm  22 . In controlling the operation of the robot arm  22  based on the position information acquired from the encoders  24 , even when general-purpose processing with a large load such as image processing is executed in the first control section  51 , it is possible to suppress deterioration in operation accuracy. 
     The first control section  51  may have an abnormality detecting function of detecting whether the interrupt signals si 4 , si 5 , si 6 , si 1 , . . . transmitted to the first control section  51  by the second control section  52  are normally transmitted and received. 
       FIG. 6  is a schematic diagram for explaining the abnormality detecting function of the first control section  51 . Specifically,  FIG. 6  is a diagram schematically showing a signal waveform of the interrupt signals si 4 , si 5 , si 6 , si 1 , . . . transmitted from the second control section  52  to the first control section  51  and flows of axial information request signal sa and axial information da. 
     The first control section  51  receives the interrupt signals si 4 , si 5 , si 6 , si 1 , . . . generated at a predetermined cycle shown in  FIG. 6  and executes, with the reception of the signals as a trigger, the acquisition processing pg 4 , pg 5 , pg 6 , pg 1 , . . . and the arithmetic operation processing pc 4 , pc 5 , pc 6 , and pc 1 , . . . explained above. The first control section  51  has a function of counting the number of received interrupt signals and collating the number with a known number of axes to thereby specify information concerning which axis the position information acquired by the first control section  51  in the acquisition processing is. An axis number specified on the inside of the first control section  51  in this way is referred to as “first control section side axis number”. For example, the axis number is  1  in the case of the first axis J 1  and is  2  in the case of the second axis J 2 . 
     On the other hand, separately from the above, the first control section  51  shown in  FIG. 6  requests the second control section  52  to transmit information concerning the axes. That is, the first control section  51  has a function of transmitting the axial information request signal sa. The second control section  52  shown in  FIG. 6  has a function of returning the axial information da to the first control section  51  based on the axial information request signal sa. For example, the second control section  52  has a function of counting the number of transmitted interrupt signals and collating the number with a known number of axes to thereby specify the axial information da. The second control section  52  returns an axis number specified on the inside of the second control section  52  to the first control section  51  as the axial information da. The transmission of the axial information request signal sa and the return of the axial information da are repeated at a predetermined interval according to the interrupt signals si 4 , si 5 , si 6 , si 1 , . . . . The axis number based on the axial information da returned from the second control section  52  in this way is referred to as “second control section side axis number” herein. 
       FIG. 7  is a table showing an example of the first control section side axis number and the second control section side axis number corresponding to the interrupt signals si 1 , si 2 , and si 3  received by the first control section  51 . In  FIG. 7 , three tables divided into a table at a normal time when the interrupt signals si 1 , si 2 , and si 3  are normally transmitted and received, a table at a noise occurrence time, and a table at a missing occurrence time are shown. 
     When receiving the interrupt signals si 1 , si 2 , and si 3 , as explained above, the first control section  51  acquires the first position information d 1 , the second position information d 2 , and the third position information d 3  through the acquisition processing pg 1 , pg 2 , and pg 3 . Therefore, at the normal time, the first control section side axis number is  1 ,  2 , and  3  and the second control section side axis number is also  1 ,  2 , and  3 . As a result, the first control section  51  collates the first control section side axis number and the second control section side axis number and, when the first control section side axis number and the second control section side axis number coincide, detects that transmission and reception of the interrupt signal si 4 , si 5 , si 6 , si 1 , . . . is normal. 
     The noise occurrence time is explained. Noise means an abnormal signal that could be misrecognized as the interrupt signals si 1 , si 2 , and si 3 . In the example shown in  FIG. 7 , an abnormal signal sx is mixed between the interrupt signal si 2  and the interrupt signal si 3 . 
     When receiving the abnormal signal sx, the first control section  51  misrecognizes the abnormal signal sx as the original interrupt signal si 3 . Accordingly, the first control section side axis number corresponding to the abnormal signal sx is  3 . On the other hand, since the second control section  52  does not transmit the interrupt signal si 3  yet at this point in time, the second control section side axis number is still  2 . Then, the first control section  51  detects a mismatch of the first control section side axis number and the second control section side axis number. Specifically, a magnitude relation indicating the first control section side axis number&gt;the second control section side axis number is detected. When detecting such a mismatch, the first control section  51  determines that the abnormal signal sx is noise. When determining in this way, the first control section  51  does not perform processing executed with reception of an interrupt signal as a trigger. Consequently, it is possible to avoid starts of acquisition processing and arithmetic operation processing at wrong timings. 
     The missing occurrence time is explained. Missing means that at least one of the interrupt signals si 1 , si 2 , and si 3  cannot be received. In  FIG. 7 , an example is shown in which, although the second control section  52  transmits the interrupt signals si 1 , si 2 , and si 3 , the first control section  51  cannot receive only the interrupt signal si 2 . 
     In this case, the first control section side axis number at timing when the interrupt signal si 2  is originally received is still  1 . On the other hand, since this timing is timing after the second control section  52  transmits the interrupt signal si 2 , the second control section side axis number is  2 . 
     The first control section side axis number at timing for receiving the interrupt signal si 3  is  2 . On the other hand, since this timing is timing after the second control section  52  transmits the interrupt signal si 3 , the second control section side axis number is  3 . 
     Then, the first control section  51  detects mismatch of the first control section side axis number and the second control section side axis number. Specifically, a magnitude relation indicating the first control section side axis number&lt;the second control section side axis number is detected. When detecting such a mismatch, the first control section  51  determines that missing of the interrupt signal si 2  has occurred. When determining in this way, the first control section  51  only has to perform processing for adding one to the first control section side axis number to match the first control section side axis number and the second control section side axis number. 
     As explained above, the robot arm  22  according to this embodiment includes the plurality of arms  221  to  226 . The robot system  1  includes the encoders  24  respectively corresponding to the arms  221  to  226 . As shown in  FIGS. 6 and 7 , the first control section  51  has a function of executing comparison processing for comparing the first control section side axis number, which is first individual information, held by the first control section  51  according to the interrupt signals si 1 , si 2 , and si 3 , and the second control section side axis number, which is second individual information requested and acquired from the second control section  52  according to the interrupt signals si 1 , si 2 , and si 3 . 
     With such a configuration, it is possible to detect noise and missing of the interrupt signals si 1 , si 2 , and si 3  by comparing the first control section side axis number and the second control section side axis number. Consequently, it is possible to prevent various kinds of processing from being continued while overlooking an abnormal interrupt signal. As a result, it is possible to prevent detection accuracy of the positions and the speeds of the axes from being deteriorated. 
     When missing of the interrupt signals si 1 , si 2 , and si 3  frequently occurs, detection accuracy of the positions and the speeds of the axes is deteriorated. Therefore, the robot system  1  may stop the operation of the robot system  1 . 
     As an example, the first control section  51  may have a function of outputting an abnormal signal when the first control section side axis number, which is the first individual information, and the second control section side axis number, which is the second individual information, are different a predetermined number of times or more as a result of the comparison processing. Consequently, the control device  5  can stop the operation of the robot system  1  based on the abnormal signal. As a result, it is possible to improve safety of the robot system  1 . 
     The output of the abnormal signal may be performed in both of or may be performed in one of the case in which noise is mixed in the interrupt signals si 1 , si 2 , and si 3  and the case in which missing occurs in the interrupt signals si 1 , si 2 , and si 3 . For example, when missing of the interrupt signals si 1 , si 2 , and si 3  occurs a predetermined number of times or more, influence on detection accuracy of the positions and the speeds of the axes is considered to be large. Therefore, it is desirable to output the abnormal signal. The predetermined number of times is not particularly limited but is set to, for example, three times or more. 
     The robot system and the control method for the robot system according to the present disclosure are explained above based on the illustrated embodiment. However, the present disclosure is not limited to this. The components of the sections can be replaced with any components having the same functions. Any other components may be added to the embodiment.