Patent Publication Number: US-2021178605-A1

Title: Proximity detection system

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The present application is a continuation application of International Application No. PCT/JP2019/008894 filed on Mar. 6, 2019, which is based on and claims priority to Japanese Patent Application No. 2018-172510 filed on Sep. 14, 2018. The contents of these applications are incorporated herein by reference in their entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a proximity detection system. 
     2. Description of the Related Art 
     Conventionally, proximity sensors that are capable of detecting the proximity of an object according to a change in the capacitance occurring between the object and the sensor, have been known. For example, Patent Document 1 discloses a technology in which electrodes are provided on both sides of a sheet-like pressure-sensitive conductive rubber so that contact pressure can be measured, and a sensor is capable of detecting the proximity of an object by measuring the ground capacitance of the surface-side electrode. By disposing this sensor to a manipulator of a robot, it is possible to detect the proximity of the manipulator to another object such as an obstacle.
     [Patent Document 1] Japanese Laid-open Patent Publication No. S63-238502   

     SUMMARY OF THE INVENTION 
     According to one aspect of the present invention, there is provided a proximity detection system including a proximity sensor that is a capacitive sensor mounted on a mounting position on a robot, the proximity sensor being configured to detect proximity between the mounting position and an object; and a shield signal output unit configured to apply a shield signal for preventing the proximity sensor from detecting proximity of another position of the robot other than the mounting position. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagram illustrating a system configuration of a proximity detection system according to an embodiment; 
         FIG. 2  is an external perspective view of a proximity sensor and a detection circuit according to an embodiment; 
         FIG. 3  is a diagram illustrating a laminated structure of a proximity sensor according to an embodiment; 
         FIG. 4  is a diagram illustrating a laminated structure of a shield electrode according to an embodiment; 
         FIG. 5  is a diagram illustrating a circuit configuration of a proximity detection system according to an embodiment; 
         FIG. 6  is a graph illustrating an example of a difference value of the capacitance that occurs in the proximity sensor when a ground comes in proximity with a first robot arm; 
         FIG. 7  is a graph illustrating an example of a difference value of the capacitance that occurs in the proximity sensor when a shield electrode comes in proximity with a first robot arm; 
         FIG. 8  is a graph illustrating an example of a difference value of the capacitance that occurs in the proximity sensor when a shield electrode comes in proximity with a first robot arm; and 
         FIG. 9  is a graph illustrating an example of adjusting a difference value of the capacitance that occurs in the proximity sensor when the shield electrode comes in proximity with the first robot arm. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In the conventional technology, for example, when a proximity sensor is provided to a robot to detect the proximity of the robot to an obstacle such as a person, when another portion of the robot is brought into proximity to the portion of the robot provided with the sensor, there is a risk that it is mistakenly detected that the robot is brought into proximity to an obstacle such as a person, and the robot may be stopped immediately. Accordingly, there is a need for a technology that can increase the accuracy in the detection of an obstacle in proximity to a robot, by preventing another portion of the robot, which may come in proximity with the portion where the sensor is provided, from being mistakenly detected as an obstacle. 
     One Embodiment 
     Hereinafter, one embodiment will be described with reference to the drawings. 
     (System Configuration of a Proximity Detection System  10 ) 
       FIG. 1  is a diagram illustrating a system configuration of the proximity detection system  10  according to an embodiment. The proximity detection system  10  illustrated in  FIG. 1  is a system for detecting the proximity of a robot  20  to a person such as a worker and outputting the detection result to a robot control device  30 . As illustrated in  FIG. 1 , the proximity detection system  10  includes a proximity sensor  11 , a detection circuit  12 , a shield electrode  13 , and a robot arm shield circuit  14 . 
     The proximity sensor  11  is a capacitive proximity sensor. The proximity sensor  11  is mounted at any position of the robot  20 , and detects the proximity of the robot  20  to an object. In the example illustrated in  FIG. 1 , the proximity sensor  11  is mounted on a first robot arm  21  of the robot  20  and detects proximity of an object associated with the motion of the first robot arm  21 . 
     The detection circuit  12  detects the proximity between the first robot arm  21  and an object by detecting a change in capacitance at the proximity sensor  11 . Specifically, the detection circuit  12  drives the proximity sensor  11  by applying an a sine-wave shaped AC voltage to the proximity sensor  11 . Incidentally, an object such as a person can be regarded as a conductor and can be regarded as being connected to the ground. Therefore, according to the proximity state between the first robot arm  21  and an object, at the proximity sensor  11 , the capacitance between the proximity sensor  11  and the object changes and the current value of the current flowing through the proximity sensor  11  changes. The detection circuit  12  can detect the proximity between the first robot arm  21  and an object based on the amount of change in the current flowing through the proximity sensor  11 . For example, when a difference value of a capacitance at the proximity sensor  11  (that is, a difference value of the current flowing through the proximity sensor  11  from a reference value, by using, as the reference value, the current value when an object such as a human body is not present in the surrounding area) exceeds a predetermined upper limit threshold value th 1 , the detection circuit  12  detects that an object is in proximity to the first robot arm  21 . Note that the upper limit threshold value th 1  is set by obtaining an actual measurement value by changing the distance between the proximity sensor and an object (conductor), and setting the upper limit threshold value th 1  based on the measurement value. The detection circuit  12  outputs a detection result of the capacitance (i.e., a value representing a change in the capacitance) to the robot control device  30  which controls the motion of the robot  20 . Alternatively, the detection circuit  12  may determine the proximity state with respect to an obstacle based on the detection result of capacitance, and output the determination result to the robot control device  30 . For example, when it is determined that “an object has come in proximity with the first robot arm  21 ” based on the detection result or the determination result output from the detection circuit  12 , the robot control device  30  performs predetermined control to be performed when the robot  20  is in close proximity to an obstacle, such as immediately stopping the operation of the robot  20 . 
     In the present embodiment, the shield electrode  13  is provided on a movable portion of the robot  20 . Specifically, the shield electrode  13  is provided on a movable portion of the robot  20 , which is a portion that may be mistakenly detected by the proximity sensor  11 . In the example illustrated in  FIG. 1 , the shield electrode  13  is mounted on a second robot arm  22  of the robot  20 . The second robot arm  22  is rotatably connected to the first robot arm  21  and is movable with respect to the first robot arm  21 . The second robot arm  22  may be mistakenly detected as an obstacle proximate to the first robot arm  21  during a series of motions of the robot. The shield electrode  13  is disposed at a position where the first robot arm and the second robot arm face each other when the first robot arm and the second robot arm are brought into proximity to each other. 
     The robot arm shield circuit  14  is an example of a “shield signal output unit”. The robot arm shield circuit  14  applies, to the shield electrode  13  provided on the second robot arm  22 , a shield signal that can cause the detection of the proximity of an object by the proximity sensor  11  to be non-detection, that is, preventing the proximity sensor  11  from detecting the proximity of an object (i.e., such that there will be almost no change in the capacitance at the proximity sensor  11 ). That is, when an object, such as a human body, which can be considered as a ground, comes in proximity with the proximity sensor  11  as described above, the capacitance value between the proximity sensor  11  and the object changes so that the current flowing to the proximity sensor  11  changes. However, by attaching the shield electrode  13  to the object so that the shield electrode  13  is interposed between the object and the proximity sensor  11 , and by applying a driving signal to the shield electrode  13  as described below, even when the object comes in proximity with the proximity sensor  11 , the proximity sensor  11  is not affected by the object that is a ground so that the change in the current value of the current flowing to the proximity sensor  11  is reduced or eliminated. Therefore, the proximity sensor  11  does not detect proximity with the object. That is, even when the second robot arm  22  comes in proximity with the first robot arm  21 , the robot arm shield circuit  14  can prevent the second robot arm  22  from being mistakenly detected as an obstacle. 
     (Configuration of the Proximity Sensor  11 ) 
       FIG. 2  is an external perspective view of the proximity sensor  11  and the detection circuit  12  according to an embodiment.  FIG. 3  is a diagram illustrating a laminated structure of the proximity sensor  11  according to an embodiment. In  FIG. 2 , the appearance of the front side (on the side with a detection electrode  302 ) of the proximity sensor  11  is illustrated. 
     The proximity sensor  11  illustrated in  FIGS. 2 and 3  is a device capable of detecting the proximity state of an object (e.g., a person, etc.). As illustrated in  FIG. 3 , the proximity sensor  11  is generally thin and sheet-like and has a laminated structure in which a plurality of members are stacked. As illustrated in  FIG. 3 , the proximity sensor  11  is attached to the surface of the first robot arm  21  at a portion on the back side thereof (on the side with a guard electrode  304 ). 
     As illustrated in  FIG. 3 , the proximity sensor  11  includes an insulating film  301 , the detection electrode  302 , a spacer  303 , the guard electrode  304 , and an insulating film  305 , in the stated order from the front side (the upper side in the figure) of the proximity sensor  11 . 
     The insulating film  301  is a film-like member formed of an insulating material. The insulating film  301  protects the surface of the detection electrode  302 . The insulating film  301  may be, for example, a PET film. 
     The detection electrode  302  is formed on the entire surface of the insulating film  301 . Further, the detection electrode  302  is electrically conductive and is formed by printing conductive ink onto the insulating film  301  and firing the conductive ink. The detection electrode  302  detects the proximity state of an object to the proximity sensor  11 . Specifically, as described above, the detection electrode  302  is driven by an AC (alternating-current) voltage applied from the detection circuit  12 , and in accordance with the proximity state of an object to the detection electrode  302 , the capacitance between the detection electrode  302  and the object (ground) changes, and in accordance with the change in the capacitance, the current value changes. The change in the current value is detected by the detection circuit  12 . The detection electrode  302  may be a thin film conductor such as, for example, ITO (Indium Tin Oxide), IZO (Indium Zinc Oxide), or a metal film (e.g., a composite material of silver, copper, aluminum, and molybdenum). 
     The spacer  303  is a sheet-like member formed of an insulating material. The spacer  303  is provided between the detection electrode  302  and the guard electrode  304 . The spacer  303  maintains a constant space between the detection electrode  302  and the guard electrode  304  and insulates the detection electrode  302  and the guard electrode  304  from each other. The spacer  303  can be, for example, a urethane foam. Also, although not illustrated, the top and the bottom of the spacer  303  are held by the insulating film  301  and the insulating film  305 , respectively, by a double-sided tape or an adhesive. 
     The guard electrode  304  is formed on the entire surface of the insulating film  305 . Further, the guard electrode  304  is electrically conductive and is formed by printing conductive ink onto the insulating film  305  and firing the conductive ink. The guard electrode  304  is provided on the bottom side of the detection electrode  302 . The guard electrode  304  is formed so as to be superimposed above the detection electrode  302  in a planar view and is formed to have a greater area than the detection electrode  302  so that the outer periphery of the guard electrode  304  protrudes out from the detection electrode  302 . The guard electrode  304  prevents the detection electrode  302  from being affected from the lower surface (the surface on the side of the first robot arm  21 ), by receiving an active shield signal having the same waveform as that applied to the detection electrode  302 , applied from the detection circuit  12 . Specifically, for example, the guard electrode  304  can prevent the capacitance at the detection electrode  302  from being affected by the capacitance with respect to the first robot arm  21 , or prevent noise from the first robot arm  21  from entering the detection electrode  302 , thereby increasing the detection accuracy of the detection electrode  302 . The guard electrode  304  may be a thin film-like conductor such as, for example, ITO (Indium Tin Oxide), IZO (Indium Zinc Oxide), or a metal film (e.g., a composite material of silver, copper, aluminum, and molybdenum). 
     The insulating film  305  is a film-like member formed of an insulating material. The insulating film  305  protects the bottom surface of the guard electrode  304 . The insulating film  305  can be, for example, a PET film. 
     (Configuration of the Shield Electrode  13 ) 
       FIG. 4  illustrates a laminated structure of the shield electrode  13  according to an embodiment. The shield electrode  13  illustrated in  FIG. 4  is a device that can cause the detection of the proximity of an object by the proximity sensor  11  to be non-detection (the shield electrode  13  can prevent the proximity sensor  11  from detecting the proximity of an object) (i.e., such that there is almost no change in the capacitance at the proximity sensor  11 , which would be caused by the proximity of an object). As illustrated in  FIG. 4 , the shield electrode  13  is generally thin and sheet-like and has a laminated structure in which a plurality of members are stacked. As illustrated in  FIG. 4 , the shield electrode  13  is attached to the surface of the second robot arm  22  at a portion on the back side thereof (on the side with an electrode  402 ). 
     As illustrated in  FIG. 4 , the shield electrode  13  includes an insulating film  401  and the electrode  402 , in the stated order from the surface side (the lower side in the figure) of the proximity sensor  11 . 
     The insulating film  401  is a film-like member formed of an insulating material. The insulating film  401  protects the surface of the electrode  402 . The insulating film  401  may be, for example, a PET film. 
     The electrode  402  is formed on the entire surface of the insulating film  401 . Further, the electrode  402  is electrically conductive and is formed by printing a conductive ink onto the insulating film  401  and firing the conductive ink. The electrode  402  receives a shield signal from the robot arm shield circuit  14 , so that even when the shield electrode  13  comes in proximity with the proximity sensor  11 , the capacitance at the proximity sensor  11  does not appreciably change, so that the proximity sensor  11  does not detect any objects. That is, even when the second robot arm  22 , on which the shield electrode  13  is mounted, comes in proximity with the first robot arm  21 , the electrode  402  can prevent the second robot arm  22  from being mistakenly detected as an obstacle. The electrode  402  may be, for example, a thin film conductor such as ITO, IZO, a metal film, a thin film-like conductor, or the like. 
     (Circuit Configuration of the Proximity Detection System  10 ) 
       FIG. 5  is a diagram illustrating a circuit configuration of the proximity detection system  10  according to an embodiment. As illustrated in  FIG. 5 , the proximity detection system  10  includes a detection control IC (Integrated Circuit)  10 A. The detection control IC  10 A includes a detecting unit  120 , a waveform generation circuit  15 , and a digital block  501 . The detecting unit  120  is connected to the detection electrode  302  of the proximity sensor  11 . The detecting unit  120  detects the proximity state of an object to the proximity sensor  11 , by measuring the current flowing through the detection electrode  302  and measuring the change in capacitance between the detection electrode  302  and an object (ground), such as a person. The digital block  501  is a block for converting the output signal from the detecting unit  120  into a digital signal, and outputs the digital signal to an MPU (microprocessor unit)  502 . The MPU  502  determines whether a person has come into proximity, and outputs the determination result to the robot control device  30 . The waveform generation circuit  15  is connected to the guard electrode  304 , the robot arm shield circuit  14 , and the detecting unit  120 . The waveform generation circuit  15  generates an active shield signal and outputs the active shield signal to the guard electrode  304  and the robot arm shield circuit  14 . The active shield signal is a signal having a waveform synchronized with a driving signal applied to the detection electrode  302  from the waveform generation circuit  15  via the detecting unit  120 . The guard electrode  304  receives the active shield signal, thereby primarily preventing the detection electrode  302  from being affected by the robot surface in the present embodiment. It is preferable that the active shield signal is a sinusoidal wave that is resistant to high frequency noise radiation and conduction noise. 
     The robot arm shield circuit  14  receives the active shield signal output from the waveform generation circuit  15 . The robot arm shield circuit  14  includes a midpoint potential forming circuit  14 A and an amplitude adjustment circuit  14 B. The midpoint potential forming circuit  14 A forms the same potential as the voltage applied to the detecting unit  120  and includes a buffer circuit (a voltage follower circuit) to supply a stable voltage for generating a shield signal to the amplitude adjustment circuit  14 B. The amplitude adjustment circuit  14 B generates a shield signal by adjusting the amplitude of the active shield signal input to the robot arm shield circuit  14  and outputs the shield signal to the shield electrode  13 . That is, the shield signal has the same frequency as the active shield signal and is different in amplitude from the active shield signal. Specifically, the amplitude adjustment circuit  14 B includes a resistor R 1  and determines the amplitude of the active shield signal based on the resistance value of the resistor R 1  and outputs the amplitude to the shield electrode  13  via a buffer circuit (a voltage follower circuit). Accordingly, the resistor R 1  used here has an appropriate resistance value so that the amplitude of the active shield signal becomes the appropriate amplitude which has been obtained in advance. 
     (Example of Difference Value of Capacitance that Occurs in the Proximity Sensor  11 ) 
       FIG. 6  is a graph illustrating an example of a difference value of the capacitance that occurs in the proximity sensor  11  when a ground (e.g., an object that corresponds to a human body, the second robot arm  22  to which the shield electrode  13  is not mounted, or the like, and that is considered to be a conductor and connected to the ground) comes in proximity with the first robot arm  21 . The reference value of the difference value is the value of the capacitance when there is no object in the surrounding area. In the graph of  FIG. 6 , the horizontal axis indicates the proximity distance of the ground to the first robot arm  21 , and the vertical axis indicates the difference value of the capacitance that occurs in the proximity sensor  11 . As illustrated in  FIG. 6 , in the proximity detection system  10  of the present embodiment, as the proximity distance of ground to the first robot arm  21  decreases, the capacitance value increases, so that the difference value of the capacitance that occurs in the proximity sensor  11  gradually increases. 
       FIG. 7  is a graph illustrating an example of the difference value of the capacitance that occurs in the proximity sensor  11  when the shield electrode  13  driven by a shield signal comes in proximity with the first robot arm  21 . The reference value of the difference value is the value of the capacitance when the shield electrode  13  is not present in the surrounding area. In the graph of  FIG. 7 , the horizontal axis indicates the proximity distance of the shield electrode  13  to the first robot arm  21 , and the vertical axis indicates the difference value of the capacitance that occurs in the proximity sensor  11 .  FIG. 7  illustrates the characteristic of the difference value of the capacitance at the proximity sensor  11  when the amplitude of the shield signal applied to the shield electrode  13  is made to be the same as the amplitude of the active shield signal applied to the guard electrode  304  (i.e., the amplitude of the shield signal is not adjusted). On the back side of the detection electrode  302  of the proximity sensor  11 , a capacitance does not occur due to the guard electrode  304 , and, therefore, the back side of the detection electrode  302  does not affect the capacitance characteristic. On the other hand, on the front side of the detection electrode  302 , a capacitance (floating capacitance) occurs between the detection electrode  302  and the ground when the shield electrode  13  is located at a distance. As illustrated in  FIG. 7 , in the proximity detection system  10  of the present embodiment, a signal similar to that applied to the detection electrode  302  is applied to the shield electrode  13 , and, therefore, the difference in potential between the detection electrode  302  and the shield electrode  13  is reduced, so that the capacitance (floating capacitance) between the detection electrode  302  and the ground is reduced. Thus, in contrast to the graph illustrated in  FIG. 6 , as the proximity distance of the shield electrode  13  to the first robot arm  21  becomes short, the difference value of the capacitance that occurs in the proximity sensor  11  gradually becomes smaller. 
     (Example of Variation of Difference Value of Capacitance that Occurs in the Proximity Sensor  11 ) 
       FIG. 8  is a graph illustrating an example of the variation of the difference value of the capacitance that occurs in the proximity sensor  11  when the shield electrode  13  comes in proximity with the first robot arm  21 . The reference value of the difference value is the value of the capacitance when the shield electrode  13  is not present in the surrounding area. As illustrated in  FIG. 8 , in the proximity detection system  10  of the present embodiment, by adjusting the amplitude of the shield signal applied to the shield electrode  13 , the difference value of the capacitance that occurs in the proximity sensor  11  when the shield electrode  13  comes in proximity with the first robot arm  21  can be varied. Specifically, by gradually decreasing the amplitude of the shield signal applied to the shield electrode  13 , the difference value of the capacitance that occurs in the proximity sensor  11  can be gradually increased. That is, by decreasing the amplitude, the shield electrode  13  becomes similar to the ground, and, therefore, the same tendency as in  FIG. 6  will occur. Conversely, by gradually increasing the amplitude of the shield signal applied to the shield electrode  13 , the difference value of the capacitance that occurs in the proximity sensor  11  can be gradually decreased, and, therefore, the same tendency as in  FIG. 7  will occur. 
     Therefore, in the proximity detection system  10  of the present embodiment, various requirements can be addressed by adjusting the amplitude of the shield signal applied to the shield electrode  13  and adjusting the difference value of the capacitance that occurs in the proximity sensor  11  when the shield electrode  13  comes in proximity with the first robot arm  21 . 
     (Example of Adjustment of Difference Value of Capacitance that Occurs in the Proximity Sensor  11 ) 
       FIG. 9  is a graph illustrating an example of adjustment of the difference value of the capacitance that occurs in the proximity sensor  11  when the shield electrode  13  comes in proximity with the first robot arm  21 , and for the sake of explanation of the graph of  FIG. 8 ,  FIG. 9  includes partially extracted data from  FIG. 8 . 
     For example, in an example in which an amplitude represented by a difference value characteristic  900  of  FIG. 9  is applied to the shield electrode  13 , in a proximity distance range r (100 mm to 260 mm), even when the second robot arm  22  comes in proximity with the first robot arm  21 , the difference value of the capacitance that occurs in the proximity sensor  11  (hereinafter simply referred to as the “difference value”) is substantially zero, which is an ideal difference value. Therefore, the influence caused by the proximity of the second robot arm  22  can be disregarded. Thus, even if the second robot arm  22  and a human body, etc., come in proximity with the proximity sensor  11  at the same time, by measuring the difference value, it is possible to detect the proximity of the human body, etc. 
     In the example illustrated in  FIG. 9 , an upper limit threshold value th 1  of the difference value is defined. The upper limit threshold value th 1  is a boundary value for determining whether the first robot arm  21  and an obstacle such as a person have come in proximity with each other. When the difference value measured by the detecting unit  120  is converted into a digital signal by the digital block  501  and exceeds the upper limit threshold value th 1  in the MPU  502 , it is determined that the first robot arm  21  and an obstacle such as a person have come in proximity with each other. 
     For example, according to a difference value characteristic  911  illustrated in  FIG. 9 , the difference value exceeds the upper limit threshold value th 1  in the proximity distance range r. In this case, by adjusting the resistance value of the resistor R 1  provided in the amplitude adjustment circuit  14 B to increase the amplitude of the shield signal applied to the shield electrode  13 , the difference value characteristic  911  can be brought closer to the ideal difference value characteristic  900 , as illustrated by the arrow A in the figure. Note that even in the case of the difference value characteristic  900 , when the proximity distance becomes 40 mm or less, erroneous detection will be performed; however, this can be addressed by setting a mechanical configuration to prevent further proximity. 
     Further,  FIG. 9  illustrates an example in which a lower limit threshold value th 2  of the difference value is defined. The lower limit threshold value th 2  is used to determine whether the second robot arm  22  has come in proximity with the first robot arm  21 . That is, if the amplitude is adjusted so that the difference value falls below the predetermined lower limit threshold value th 2  at a predetermined proximity distance, as the difference value characteristics  901  and  912  illustrated in  FIG. 9 , it can be determined whether the second robot arm  22  has come into proximity. However, in this case, when the shield electrode  13  and the human body, etc., have come in proximity with the proximity sensor  11  at the same time, the output becomes smaller as compared to the case where only a human body, etc., has come in proximity with the proximity sensor  11 . Therefore, it is necessary to set the upper limit threshold value th 1  by which it is determined that a human body, etc., has come into proximity, to be low. 
     In the actual setting, the amplitude and threshold values are set appropriately based on the difference value of the proximity sensor  11  when only the shield electrode  13  of  FIG. 9  is in proximity with the proximity sensor  11 , the difference value of the proximity sensor  11  when only the human body, etc., of  FIG. 6  is in proximity with the proximity sensor  11 , the difference value when both the shield electrode  13  and the human body, etc., of  FIG. 9  and  FIG. 6  are in proximity with the proximity sensor  11 , and what is to be determined in what case, etc. 
     Further, the relationship between the amplitude of the shield signal and the difference value of the capacitance that occurs in the proximity sensor  11  varies depending on the product specification (e.g., the size of the shield electrode  13 , etc.). Therefore, it is preferable to derive an appropriate amplitude according to the specification of the product as the amplitude of the shield signal by simulation or the like. 
     As described above, the proximity detection system  10  according to an embodiment includes the proximity sensor  11  that is a capacitive sensor, which is mounted on the first robot arm  21  of the robot  20  (an example of “a mounting position” that is any position on a robot), for detecting the proximity of an object to the first robot arm  21 ; and the robot arm shield circuit  14  for applying, to the second robot arm  22  of the robot  20  (an example of “another position of the robot other than the mounting position”), a shield signal capable of preventing the proximity sensor  11  from detecting the proximity of the second robot arm. Accordingly, the proximity detection system  10  according to an embodiment can prevent the second robot arm  22  from being detected by the proximity sensor  11  even when the second robot arm  22  is proximate to the first robot arm  21 . Thus, by the proximity detection system  10  according to an embodiment, the detection accuracy of an obstacle coming in proximity with the robot  20  can be increased. 
     The proximity detection system  10  according to an embodiment further includes the shield electrode  13  provided on the second robot arm  22 , and the robot arm shield circuit  14  applies a shield signal to the shield electrode  13 . That is, by the proximity detection system  10  according to an embodiment, any position of the robot  20  can be easily set to be a target position for preventing erroneous detections by the sensor, by providing a shield electrode to the corresponding position. 
     Further, in the proximity detection system  10  according to an embodiment, the robot arm shield circuit  14  generates a shield signal by adjusting the amplitude of an input signal having a waveform synchronized with a driving signal applied to the proximity sensor  11 . That is, the proximity detection system  10  according to an embodiment can use the driving signal applied to the proximity sensor  11  to generate a shield signal, and thus can generate a shield signal with a relatively simple configuration. 
     Further, in the proximity detection system  10  according to an embodiment, the proximity sensor  11  includes the detection electrode  302  for detecting the proximity of an object to the robot  20  and the guard electrode  304  provided so as to be superimposed above the detection electrode  302 , and the robot arm shield circuit  14  generates a shield signal by using an active shield signal applied to the guard electrode  304  as an input signal and adjusting the amplitude of the input signal. Accordingly, in the proximity detection system  10  according to an embodiment, the guard electrode  304  is provided in the proximity sensor  11 , so that the detection accuracy by the detection electrode  302  can be increased, and a shield signal can be generated by using the active shield signal applied to the guard electrode  304 . Therefore, the shield signal can be generated by a relatively simple configuration. 
     Further, in the proximity detection system  10  according to an embodiment, the robot arm shield circuit  14  generates a shield signal by adjusting the amplitude of an input active shield signal such that the difference value of the capacitance detected by the proximity sensor  11  does not exceed the predetermined upper limit threshold value th 1  in the predetermined proximity distance range r with respect to the proximity sensor  11 , when the second robot arm  22  comes in proximity with the proximity sensor  11 . Accordingly, the proximity detection system  10  according to an embodiment can prevent the second robot arm  22  from being detected by the proximity sensor  11  even when the second robot arm  22  has come in proximity with the first robot arm  21 . 
     While an embodiment of the present invention has been described in detail above, the present invention is not limited to these embodiments, and various modifications or variations are possible within the scope of the invention as defined in the appended claims. 
     For example, in the above described embodiment, one proximity sensor  11  is provided to the robot  20 , but the embodiment is not limited thereto. A plurality of the proximity sensors  11  may be provided to the robot  20 . 
     For example, in the above described embodiment, one shield electrode  13  is provided for the robot  20 , but the embodiment is not limited thereto. A plurality of the shield electrodes  13  may be provided for the robot  20 . 
     For example, in the above-described embodiment, the second robot arm  22  is provided with the shield electrode  13  and a shield signal is applied to the shield electrode  13 , but the embodiment is not limited thereto. The shield electrode  13  may not be provided to the second robot arm  22 , and a shield signal may be applied directly to a conductive portion (for example, a metal surface) of the second robot arm  22 . 
     Further, in the above-described embodiment, the proximity sensor  11  is provided at a movable portion, that is, the first robot arm  21 , in order to prevent the proximity of the first robot arm  21  to human body or the like from being equal to or more than a predetermined value, but the embodiment is not limited thereto. The proximity sensor  11  may be provided at a fixed portion to stop the operation of the robot  20  when a human body or the like comes into proximity within a predetermined distance. 
     Further, in the embodiment described above, the shield electrode  13  is provided at the second robot arm  22  which is a movable portion, but the shield electrode  13  may be provided at any portion of the robot  20  which may come in proximity with the proximity sensor  11 . For example, when the proximity sensor  11  is provided at a movable portion, the shield electrode  13  may be mounted at both a movable portion and a fixed portion, and when the proximity sensor  11  is provided at a fixed portion, the shield electrode  13  may be mounted at a movable portion. 
     According to an aspect of the present invention, the detection accuracy of the proximity between a robot and an obstacle can be increased because another position of the robot other than a position where a sensor is mounted, can be prevented from being mistakenly detected as an obstacle. 
     Although the embodiments have been described in detail, the present invention is not limited to specific embodiments, and various modifications and changes can be made within the scope set forth in the appended claims.