Patent Publication Number: US-2023140740-A1

Title: Hand system and hand

Description:
FIELD 
     The present invention relates to a hand technology, and in particular, relates to a hand system and hand which can execute workpiece extraction detection with few restrictions. 
     BACKGROUND 
     As pick-and-place hands, various hands such as a multi-finger grip type, electromagnetic suction type, vacuum suction type, and Bernoulli type hands are known. When using these hands to extract sheet-like air-permeable workpieces such as meshes, it may not be possible to extract a workpiece with a multi-finger grip type hand due to a lack of wall thickness. In electromagnetic suction type hands, the workpiece is limited to magnetic materials. In vacuum suction type hands, air can leak through the workpiece, whereby vacuum pressure cannot be maintained and the workpiece cannot be suctioned. Thus, in the case of such sheet-shaped air-permeable workpieces, it is common to use a Bernoulli-type hand that suctions workpieces by negative pressure generated by the ejection of compressed air. As technologies related to these hands, the following literature is known. 
     Patent Literature 1 describes an air-permeable workpiece removal/retention device which can extract stacked air-permeable workpieces one by one and securely retain an air-permeable workpiece by vacuum suction by suctioning the air-permeable workpieces in a non-contact manner using the suction force generated by the ejection of compressed air from a compressed air ejection nozzle and vacuum suctioning and holding the extracted air-permeable workpieces with a vacuum suction nozzle. 
     Patent Literature 2 describes a separating device which lifts and separates stacked sheet-shaped magnetic materials by electromagnetic attraction, wherein there is provided an eddy current-type thickness detection mechanism in which an excitation coil which generates a high-frequency magnetic field is arranged near one end surface of the sheet-shaped magnetic material and a detection coil which detects the impedance of the sheet-like magnetic materials is arranged near the other end face of the sheet-like magnetic material. 
     Patent Literature 3 describes a photomask antistatic method, wherein in order to monitor and detect with an electrical resistance measurement device that a conductive film has been reached by driving two conductive pins into the photomask, resistance detection pins connected to the electrical resistance measurement device are arranged side by side on a suction pad, and when the conductive pins come into contact with the suction pad, the resistance detection pins make electrical contact with the conductive pins. 
     CITATION LIST 
     Patent Literature 
     
         
         [PTL 1] Japanese Unexamined Patent Publication (Kokai) No. 2003-54774 
         [PTL 2] Japanese Unexamined Patent Publication (Kokai) No. 2010-254438 
         [PTL 3] Japanese Unexamined Patent Publication (Kokai) No. 11-67647 
       
    
     SUMMARY 
     Technical Problem 
     When extracting a workpiece with a hand, in some cases, the workpiece cannot be extracted, and in some cases, when attempting to extract a single workpiece, a plurality of workpieces are extracted or the gripping state thereof is not suitable. Though an electromagnetic induction type sensor, an image recognition sensor, or the like can be used for detecting the extraction of workpieces (detection of the number of workpieces extracted, detection of the gripping state, etc.), there are problems as described below, and they may not be applicable. 
     Though electromagnetic induction-type contact sensors generate a magnetic field to magnetize a workpiece and measure the amount of magnetic flux of the magnetic field generated in the workpiece to detect the extraction of the workpiece, the workpiece is limited to magnetic materials. Furthermore, though such sensors are suitable for workpieces having a flat surface with good adhesion to the sensor, measurement cannot be accurately performed on workpieces having poor adhesion such as wrinkles or unevenness. Furthermore, in two-head type electromagnetic induction non-contact sensors, a workpiece is inserted between north and south pole magnets, an eddy current is generated in the workpiece, and the amount of magnetic flux of the magnetic field generated by the eddy current is measured, but the workpiece is limited to sheet-shaped flat plate workpieces. 
     Conversely, in image recognition sensors such as cameras, it is necessary to switch parameters for image recognition and error determination in accordance with the shape of the workpiece and the surrounding environment, which is complicated. Furthermore, in the case of sheet-shaped workpieces, if the workpieces are in close contact with each other in a state where the outer shapes are aligned, it may not be possible to determine whether one workpiece or a plurality of workpieces have been extracted. Further, in image recognition sensors, the entire system becomes expensive, whereby the hand system becomes expensive. 
     Thus, there is a need for a hand technology which can execute workpiece extraction detection with few restrictions. 
     Solution to Problem 
     An aspect of the present disclosure provides a hand system, comprising a suction pad configured to suction a conductive workpiece by the fluid effect, at least three electrodes arranged on the suction pad, and an electric characteristic measurement instrument configured to measure the electrical characteristics of an electric circuit formed by contact between any two of the electrodes and the workpiece. 
     Another aspect of the present disclosure provides a hand, comprising a suction pad configured to suction a conductive workpiece by the fluid effect, and an electrode which protrudes from a suction surface of the suction pad and which is capable of ascending in response to contact with the workpiece. 
     Yet another aspect of the present disclosure provides a hand, comprising a suction pad configured to suction a conductive workpiece by the fluid effect, at least three electrodes arranged on the suction pad, and a rotary contact with is capable of switching contact with any two of the electrodes. 
     Advantageous Effects of Invention 
     According to the aspect of the present disclosure, by providing the hand with at least three electrodes, the gripping state of the workpiece can be detected. Furthermore, by measuring the electrical characteristics of an electric circuit formed by contact between any two of the electrodes and the workpiece, the number of extracted workpieces can be detected. Since the extraction of the workpiece is detected by measuring the electrical characteristics, the workpiece is not limited to magnetic materials and it is sufficient that it be a conductor. Furthermore, the extraction of workpieces can be detected even if the workpieces are in close contact with each other in a state where the outer shapes thereof match. Thus, the workpiece extraction detection (detection of the number of extractions, detection of the gripping state, etc.) can be executed with few restrictions. 
     According to the other aspect of the present disclosure, since the electrode protrudes from the suction pad, workpiece extraction detection can be executed even with a Bernoulli-type hand which retains a workpiece in a non-contact manner. Furthermore, even if the workpiece has poor adhesiveness, such as if it has wrinkles or unevenness, since the electrode can ascend, depending on the shape of the workpiece, workpiece extraction detection can be executed with few restrictions. 
     According to the yet other aspect of the present disclosure, since the rotary contact can switch contact to any two of the electrodes, even if the number of electrodes increases, the electrical characteristic value between any electrodes can be measured with only one electric characteristic measurement instrument. As a result, workpiece extraction detection can be executed with few restrictions. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG.  1    is a perspective view showing a hand system and hand according to an embodiment. 
         FIG.  2 A  is a bottom view showing a bottom surface of a suction pad according to an embodiment. 
         FIG.  2 B  is a partial cross-sectional view showing a cross-section of the suction pad according to an embodiment taken along line A-A. 
         FIG.  3 A  is a partial cross-sectional view showing a cross-section of a suction pad comprising face-aligned electrodes. 
         FIG.  3 B  is a partial cross-sectional view showing the cross-section of a suction pat comprising a protruding electrode which is capable of ascending. 
         FIG.  4    is a block diagram showing an example of a control structure of a hand system. 
         FIG.  5    is a block diagram showing an example of an electric circuit when there are three electrodes. 
         FIG.  6    is a flowchart showing an operation example of a hand system. 
         FIG.  7    is a block diagram showing an example of an electric circuit when there are four electrodes. 
         FIG.  8    is a plan view showing an example of the structure of a rotary contact when there are three electrodes. 
         FIG.  9    is a plan view showing an example of the operation of the rotary contact when there are three electrodes. 
         FIG.  10    is a plan view showing an example of the structure of a rotary contact when there are four electrodes. 
     
    
    
       FIG.  11    is a plan view showing an example of the operation of the rotary contact when there are four electrodes. 
     DESCRIPTION OF EMBODIMENTS 
     The embodiments of the present disclosure will be described in detail below with reference to the attached drawings. In the drawings, identical or similar constituent elements have been assigned the same or similar reference signs. Furthermore, the embodiments described below do not limit the technical scope of the invention described in the claims or the definitions of the terms. 
       FIG.  1    shows a hand system  1  according to the present embodiment. The hand system  1  comprises a hand  10  which extracts workpieces W, and a transport device  20  which transports extracted workpieces W to predetermined locations. As long as the workpieces W are conductive workpieces, they may be, for example, air-permeable workpieces such as metal meshes, or air-impermeable workpieces such as conductive films for touch panels. Though the workpiece W is a sheet-shaped workpiece having no wall thickness, it may have a thick wall as long as it is relatively lightweight. Though the workpieces W are stacked on a mounting device  50 , they need not necessarily be stacked. The mounting device  50  may be a fixedly installed workpiece stocker, or may be a movable mounting device such as a conveyor, a shuttle, or an automatic guided vehicle. The hand  10  is a Bernoulli-type hand that suctions workpieces W by the Bernoulli effect, or may be a vacuum suction type hand. The hand  10  comprises a palm  11  attached to the end of the transport device  20  and a suction pad  12  affixed to the palm  11  for suctioning workpieces W by the fluid effect. The hand  10  further comprises at least three electrodes  13  arranged on the suction pad  12 (refer to  FIGS.  2 A and  2 B ), and an electric characteristic measurement instrument  16  which measures the electrical characteristics of an electric circuit formed by contact between any two of the electrodes  13  and a workpiece W. The transport device  20  is an industrial robot such as an articulated robot or a parallel link type robot, or may be a transport device such as a loader, a shuttle, or an automatic guided vehicle. 
       FIG.  2 A  shows the bottom surface of the suction pad  12 , and  FIG.  2 B  shows the cross-section of the suction pad  12  of  FIG.  2 A  taken along line A-A. In the case of a Bernoulli-type hand, the suction pad  12  may be a non-contact pad comprising a nozzle  12   a  which ejects a fluid such as compressed air, and in the case of vacuum suction-type hand, a suction pad which comprises a nozzle which generates vacuum pressure between the workpiece and the suction pad  12  may be used. In the case of Bernoulli-type hands, by arranging a plurality of nozzle holes  12   b  at equal intervals on the peripheral side surface of the nozzle  12   a , a fluid such as compressed air is ejected from the nozzle hole  12   b  in the outer peripheral direction to generate a negative pressure region having a pressure lower than atmospheric pressure directly under the nozzle  12   a , whereby the suction pad  12  suctions workpieces in a non-contact manner. 
     The electrodes  13  are connected to the electric characteristic measurement instrument  16  (refer to  FIG.  1   ) via respective electrical lines  14 . The electric characteristic measurement instrument  16  measures the electrical characteristics of an electric circuit formed by contact between any two electrodes  13  and a workpiece. The electrical characteristics may be, for example, electrical resistance, but may also be electrical conductivity, current, or the like. By measuring the electrical characteristics, it becomes possible to detect the number of workpieces extracted. For example, when one metal mesh workpiece is extracted as shown in  FIG.  1   , the electric resistance becomes approximately 0.8Ω, and when two are extracted together, the electric resistance becomes approximately 0.4Ω, and when three are extracted, the electrical resistance becomes approximately 0.3Ω. Specifically, as the number of meshes increases, the electric resistance decreases (or the electric conductivity or the current increases), whereby the number of workpieces extracted can be detected. 
     It is preferable that the electrodes  13  be arranged at equal intervals in the circumferential direction of the suction pad  12 , and in particular, the outer peripheral direction of the nozzle  12   a . By providing at least three electrodes  13 , the quality of the gripping state of the workpiece can be detected. For example, when a workpiece can be detected with any combination of the electrodes  13 , it can be determined that the gripping state of the workpiece is suitable; when a workpiece can be detected with some combinations of the electrodes  13 , it can be determined that the gripping state of the workpiece is not suitable; and when a workpiece cannot be detected by any combination of the electrodes  13 , it can be determined that a workpiece has not been extracted. Since the extraction of workpieces can be detected (detection of the number of extracted workpieces, detection of the gripping state, etc.) by measuring the electrical characteristics in this manner, the workpiece may be a conductor as well as a magnetic material. Furthermore, the extraction of workpieces can be detected even if the workpieces are in close contact with each other in a state where the outer shapes align. Thus, workpiece extraction detection can be executed with few restrictions. 
     The hand  10  may further comprise a position deviation suppression pad  15  which suppresses position deviation of the workpiece when the workpiece is suctioned. The position deviation suppression pad  15  is preferably composed of a flexible material such as soft rubber or sponge and has a surface roughness or a high coefficient of friction by which workpieces do not move relative thereto. The surface  15   a  of the position deviation suppression pad  15  preferably protrudes from the suction surface  12   c  of the suction pad  12 . This makes it possible to suppress lateral displacement of a workpiece with respect to the suction pad  12  without damaging the workpiece. 
     The tips of the electrodes  13  preferably protrudes at least from the suction surface  12   c  of the suction pad  12 , or when the position deviation suppression pad  15  is provided, protrudes from the surface  15   a  of the position deviation suppression pad  15 . As a result, the extraction of workpieces can be detected even with a Bernoulli-type hand which holds workpieces in a non-contact manner. Furthermore, in the case of a vacuum suction-type hand which suctions and holds workpieces, the tips of the electrodes  13  may be positioned along the suction surface  12   c  of the suction pad  12  or the surface  15   a  of the position deviation suppression pad  15 . 
     In addition, it is preferable that the electrodes  13  be capable of ascending in response to contact with a workpiece. For example, it is preferable that electrode tubes  13   a  in which the electrodes  13  are stored be prepared, springs  13   b  be arranged in the electrode tubes  13   a  so that the electrodes  13  are biased by the springs  13   b , the electrode tubes  13   a  be locked to the side wall, etc., of the suction pad  12  with locking members  13   c , and the electrodes  13  project from the suction surface  12   c  of the suction pad  12  or the surface  15   a  of the position deviation suppression pad  15 . As a result, the electrodes  13  retract (i.e., ascends) into the suction pad  12  while being biased by the springs  13   b  in response to contact with a workpiece, and the workpiece contacts both the electrodes  13  and the position deviation suppression pads  15 . Since the electrodes  13  can ascend in accordance with the shape of the workpiece, even for workpieces having poor adhesion such as wrinkles or unevenness, workpiece extraction detection can be executed with few restrictions. 
       FIG.  3 A  shows a partial cross section of the suction pad  12  having face-aligned electrodes  13 , and  FIG.  3 B  shows a partial cross section of the suction pad  12  having protruding electrodes  13  which are capable of ascending. As shown in  FIG.  3 A , for the electrodes  13  positioned along the suction surface  12   c  of the suction pad  12  or the surface  15   a  of the position deviation suppression pad, the electrodes  13  may not contact a wrinkled workpiece W. and in this case, the extraction of the workpiece W cannot be detected. Conversely, as shown in  FIG.  3 B , for the electrodes  13  which protrude from the suction surface  12   c  of the suction pad  12  or the surface  15   a  of the position deviation suppression pad and which can ascend in the direction of the arrow, even ifthe workpiece W has poor adhesion such as wrinkles or unevenness, the electrodes  13  can ascend in accordance with the shape of the workpiece, whereby the extraction of the workpiece W can be detected. 
       FIG.  4    shows an example of the control configuration of the hand system  1 . The hand system  1  further comprises a controller  30  which controls the hand  10  and the transport device  20 . The controller  30  is a computer device comprising a processor such as a CPU (central processing unit), FPGA (field-programmable gate array), or ASIC (application specific integrated circuit), or is a semiconductor integrated circuit. The controller  30  comprises a determination unit  31  which determines the extraction and detection of workpieces (detection of the number of extracted pieces, detection of the gripping state, etc.) based on electrical characteristics, a fluid control unit  33  which controls a fluid regulator  17  based on the determination result of the determination unit  31 , and a transport control unit  32  which controls the transport device  20  based on the determination result of the determination unit  31 . 
     For example, it is preferable that the determination unit  31  determine the number of workpieces extracted by comparing the measured value of the electrical characteristics between any two electrodes  13  with a reference value, or determine the quality of the gripping state of a workpiece by a combination of the comparisons of the measured value of the electrical characteristics between any two electrodes  13  with the reference value.  FIG.  5    shows an example of an electric circuit when there are three electrodes. In this example, the hand  10  comprises three electric characteristic measurement instruments, a first electric characteristic measurement instrument  16  measures an electrical characteristic value (first characteristic value) between electrodes A and B, a second electric characteristic measurement instrument  16  measures an electrical characteristic value (second characteristic value) between electrodes B and C, and a third electric characteristic measurement instrument  16  measures the electrical characteristic value (third characteristic value) between electrodes C and A. Note that in  FIG.  5   , the thick solid lines represent the electrical lines on the positive electrode side and the thin solid lines represent the electrical lines on the negative electrode side. The first to third characteristic values are read by the controller  30  (determination unit  31 ) and appropriately used. It is preferable that the determination unit  31  determine the number of workpieces extracted and the quality of the gripping state of the workpiece using the first to third characteristic values, for example, according to the logic determination formulas shown in the following table. 
     
       
         
           
               
               
             
               
                 TABLE 1 
               
               
                   
               
               
                   
                 Determination 
               
               
                 Logic Determination Formula 
                 Result 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
            
               
                 Measured characteristic value between electrodes B-C &lt; reference 
                 Multiple 
               
               
                 characteristic value between electrodes B-C ∪ measured 
                 workpieces 
               
               
                 characteristic value between electrodes C-A &lt; reference characteristic 
                 extracted 
               
               
                 value between electrodes C-A ∪ measured characteristic value 
               
               
                 between electrodes A-B &lt; reference characteristic value between 
               
               
                 electrodes A-B 
               
            
           
           
               
               
               
            
               
                 Ex) 
                 second characteristic value between electrodes B-C = 0.5 Ω or 
                   
               
            
           
           
               
               
            
               
                 less, reference characteristic value between electrodes B-C = 0.8 Ω 
                   
               
            
           
           
               
               
               
            
               
                   
                 second characteristic value between electrodes C-A = 0.5 Ω or 
                   
               
            
           
           
               
               
            
               
                 less, reference characteristic value between electrodes C-A = 0.8 Ω 
                   
               
            
           
           
               
               
               
            
               
                   
                 second characteristic value between electrodes A-B = 0.5 Ω or 
                   
               
            
           
           
               
               
            
               
                 less, reference characteristic value between electrodes A-B = 0.8 Ω 
                   
               
               
                 Measured characteristic value between electrodes B-C ≥ reference 
                 Zero 
               
               
                 characteristic value between electrodes B-C ∩ measured 
                 workpieces 
               
               
                 characteristic value between electrodes C-A ≥ reference characteristic 
                 extracted 
               
               
                 value between electrodes C-A ∩ measured characteristic value 
               
               
                 between electrodes A-B ≥ reference characteristic value between 
               
               
                 electrodes A-B 
               
            
           
           
               
               
               
            
               
                 Ex) 
                 measured characteristic value between electrodes B-C = 1.0 × 
                   
               
            
           
           
               
               
            
               
                 10 2  Ω or more, reference characteristic value between electrodes B-C = 0.8 Ω 
                   
               
            
           
           
               
               
               
            
               
                   
                 measured characteristic value between electrodes C-A = 1.0 × 
                   
               
            
           
           
               
               
            
               
                 10 2  Ω or more, reference characteristic value between electrodes C-A = 0.8 Ω 
                   
               
            
           
           
               
               
               
            
               
                   
                 measured characteristic value between electrodes A-B = 1.0 × 
                   
               
            
           
           
               
               
            
               
                 10 2  Ω or more, reference characteristic value between electrodes A-B = 0.8 Ω 
                   
               
               
                 Measured characteristic value between electrodes B-C ≥ reference 
                 One workpiece 
               
               
                 characteristic value between electrodes B-C ∩ measured 
                 extracted; 
               
               
                 characteristic value between electrodes C-A ≥ reference characteristic 
                 gripping state 
               
               
                 value between electrodes C-A ∩ measured characteristic value 
                 unsuitable 
               
               
                 between electrodes A-B ≈ reference characteristic value between 
               
               
                 electrodes A-B 
               
            
           
           
               
               
               
            
               
                 Ex) 
                 measured characteristic value between electrodes B-C = 1.0 × 
                   
               
            
           
           
               
               
            
               
                 10 2  Ω or more, reference characteristic value between electrodes B-C = 0.8 Ω 
                   
               
            
           
           
               
               
               
            
               
                   
                 measured characteristic value between electrodes C-A = 1.0 × 
                   
               
            
           
           
               
               
            
               
                 10 2  Ω or more, reference characteristic value between electrodes C-A = 0.8 Ω 
                   
               
            
           
           
               
               
               
            
               
                   
                 measured characteristic value between electrodes A-B = 0.7 to 
                   
               
            
           
           
               
               
            
               
                 0.9 Ω or more, reference characteristic value between electrodes A-B = 0.8 Ω 
                   
               
               
                 Measured characteristic value between electrodes B-C ≈ reference 
                 One workpiece 
               
               
                 characteristic value between electrodes B-C ∩ measured 
                 extracted; 
               
               
                 characteristic value between electrodes C-A ≈ reference characteristic 
                 gripping state 
               
               
                 value between electrodes C-A ∩ measured characteristic value 
                 suitable 
               
               
                 between electrodes A-B ≈ reference characteristic value between 
               
               
                 electrodes A-B 
               
            
           
           
               
               
               
            
               
                 Ex) 
                 measured characteristic value between electrodes B-C = 0.7 to 
                   
               
            
           
           
               
               
            
               
                 0.9 Ω, reference characteristic value between electrodes B-C = 0.8 Ω 
                   
               
            
           
           
               
               
               
            
               
                   
                 measured characteristic value between electrodes C-A = 0.7 to 
                   
               
            
           
           
               
               
            
               
                 0.9 Ω, reference characteristic value between electrodes C-A = 0.8 Ω 
                   
               
            
           
           
               
               
               
            
               
                   
                 measured characteristic value between electrodes A-B = 0.7 to 
                   
               
            
           
           
               
               
            
               
                 0.9 Ω, reference characteristic value between electrodes A-B = 0.8 Ω 
               
               
                   
               
            
           
         
       
     
     Referring again to  FIG.  4   , the fluid control unit  33  preferably transmits a fluid flow pressure or flow rate adjustment command to the fluid regulator  17  in accordance with the number of workpieces extracted detected by the determination unit  31 . The fluid regulator  17  may be, for example, a solenoid valve capable of adjusting the flow pressure or flow rate of the fluid, and preferably is arranged on an air tube connected to the suction pad. The fluid regulator  17  adjusts the flow pressure or flow rate of the fluid based on the adjustment command of the fluid control unit  33 . For example, it is preferable that the fluid regulator  17  reduce the flow pressure or flow rate of the fluid when the extraction of multiple workpieces is detected, and increase the flow pressure or flow rate of the fluid when the extraction of zero workpieces is detected. It is preferable that the fluid regulator  17  repeatedly adjust the flow pressure or flow rate until the number of workpieces becomes one. 
     The transport control unit  32  preferably transmits a command for adjusting the transport speed of the workpiece to the transport device  20  in accordance with the quality of the gripping state of the workpiece detected by the determination unit  31 . The transport device  20  adjusts the transport speed of the workpiece based on the adjustment command of the transport control unit  32 . For example, it is preferable that the transport device  20  reduce the transport speed of the workpiece when a defect in the gripping state of the workpiece is detected, and increase the transport speed of the workpiece when a suitable gripping state of the workpiece is detected. 
       FIG.  6    shows an operation example of the hand system. First, as a preliminary preparation, (1) the reference characteristic value of an electric circuit formed by contact between any two electrodes  13  and one workpiece is measured and set in the controller  30  (determination unit  31 ), and (2) a reference flow pressure or reference flow rate necessary to suction one workpiece is measured and set in the controller  30  (determination unit  31 ). 
     In step S 10 , when the operator inputs a workpiece product type number into the controller  30 , the controller  30  reads a preset reference characteristic value and reference flow pressure or reference flow rate. In step S 11 , the controller  30  moves the transport device  20  to the upper surface of the workpiece. In step S 12 , the controller  30  lowers the transport device  20  and moves it to the workpiece extraction position. In step S 13 , the controller  30  adjusts the fluid regulator  17  to the reference flow pressure or the reference flow rate in accordance with the workpiece product type number to generate a suction force. 
     In step S 14 , the controller  30  determines the number of workpieces extracted based on the electrical characteristics between any two of the electrodes  13 . When it is detected in step S 14  that zero workpieces have been extracted, the fluid regulator  17  increases the flow pressure or flow rate of the fluid to increase the suction force of the workpiece in step S 15 . When it is detected that a plurality of workpieces have been extracted in step S 14 , the fluid regulator  17  reduces the flow pressure or flow rate of the fluid to reduce the suction force of the workpiece in step S 16 . Then, returning to step S 14 , the controller  30  again determines the number of workpieces extracted based on the electrical characteristics between any two of the electrodes  13 . The processes of steps S 14  to S 16  are repeated until one workpiece is extracted. 
     When the extraction of one workpiece is detected in step S 14 , the process proceeds to step S 17 , and the controller  30  determines whether the gripping state of the workpiece is suitable or unsuitable based on the combination of electrical characteristics between any two of the electrodes  13 . When a defect in the gripping state is detected in step S 17 , the process proceeds to step S 18 , and the transport speed of the workpiece is reduced so that the workpiece is not shaken off of the transport device  20  during transport. When a suitable gipping state is detected in step S 17 , the process proceeds to step S 19 , and the transport device  20  increases the transport speed of the workpiece so that the workpiece is transported at high speed during transport. In step S 20 , the transport device  20  then transports the workpiece to the predetermined location. Note that the determination of the number of workpieces extracted in step S 14  and the determination of the quality of the gripping state in step S 17  may be performed simultaneously. 
       FIG.  7    shows an example of an electric circuit when there are four electrodes. In this example, the hand  10  comprises four electric characteristic measurement instruments. A first electric characteristic measurement instrument  16  measures a first characteristic value between electrodes A and D, a second electric characteristic measurement instrument  16  measures a second characteristic value between electrodes D and C, a third electric characteristic measurement instrument  16  measures a third characteristic value between electrodes A and C, a fourth electric characteristic measurement instrument  16  measures a fourth characteristic value between electrodes A and B, a fifth electric characteristic measurement instrument  16  measures a fifth characteristic value between electrodes D and B. and a sixth electric characteristic measurement instrument  16  measures a sixth characteristic value between electrodes C and B. Note that in  FIG.  7   , the thick solid lines represent the electrical lines on the positive electrode side, and the thin solid lines represent the electrical lines on the negative electrode side. The first to sixth characteristic values are read by the controller  30  (determination unit  31 ) and appropriately used. In such an electric circuit configuration, as the number of electrodes increases, the number of electric characteristic measurement instruments becomes significant. Thus, it is desirable that the hand  10  have a configuration (for example, a rotary contact described later) in which contact can be instantaneously switched to any two electrodes and the electrical characteristic values can be measured by one electrical characteristics value measuring device. 
       FIG.  8    shows a configuration example of a rotary contact  40  when there are three electrodes  13 . The rotary contact  40  comprises a plurality of terminals  40   a ,  40   b  having predetermined central angles depending on the arrangement of the electrodes  13 . For example, when the three electrodes  13  are arranged at equal intervals in the circumferential direction of the suction pad  12 , it is preferable that the rotary contact  40  have two terminals  40   a ,  40   b  having a central angle of 120°. Note that in  FIG.  8   , the black arrow represents the terminal  40   a  on the positive electrode side, and the gray arrow represents the terminal  40   b  on the negative electrode side. The rotary contact  40  is configured such that the rotation angle is controlled by a drive source (not illustrated) such as a motor, and the contact is instantaneously switched to any two of the electrodes  13 . It is preferable that the drive source be controlled by the controller  30 . 
       FIG.  9    shows an operation example of the rotary contact  40  when there are three electrodes  13 . For example, in the initial state, the rotary contact  40  is positioned at a rotation angle that does not contact any of the electrodes  13 . When the suction pad  12  suctions a workpiece, the contact of the rotary contact  40  is switched to between electrodes A and B and the electrical characteristic value (first characteristic value) is measured, next the contact of the rotary contact  40  is switched between electrodes B and C and the electrical characteristic value (second characteristic value) is measured, and subsequently, the contact of the rotary contact  40  is switched between electrodes C and A and the electrical characteristic value (third characteristic value) is measured. Since the rotary contact  40  can switch contact to any two of the electrodes  13  in this manner, even if the number of electrodes  13  increases, three characteristic values (first to third characteristic values) can be measured with only one electric characteristic measurement instrument  16 . As a result, workpiece extraction detection can be executed with few restrictions. 
       FIG.  10    shows a configuration example of the rotary contact  40  when there are four electrodes  13 . For example, when the four electrodes  13  are arranged at equal intervals in the circumferential direction of the suction pad  12 , it is preferable that the rotary contact  40  comprise two terminals  41   a ,  41   b  having a central angle of 90° and two terminals  42   a ,  42   b  having a central angle of 180°. Note that in  FIG.  10   , the black arrows represent the terminals  41   a ,  41   b  on the positive electrode side, and the gray arrows represent the terminals  42   a ,  42   b  on the negative electrode side. The rotation angle of the rotary contact  40  is controlled by a drive source (not illustrated) such as a motor, and the contact is instantaneously switched to any two of the electrodes  13 . It is preferable that the drive source may be controlled by the controller  30 . 
       FIG.  11    shows an operation example of the rotary contact  40  when there are four electrodes  13 . For example, in the initial state, the rotary contact  40  is positioned at a rotation angle that does not contact any of the electrodes  13 . When the suction pad  12  suctions a workpiece, the contact of rotary contact  40  is switched between electrodes B and C and the electrical characteristic value (sixth characteristic value) is measured, the contact of the rotary contact  40  is next switched between electrodes B and D and the electrical characteristic value (fifth characteristic value) is measured, the contact of the rotary contact  40  is switched between electrodes C and D and the electrical characteristic value (second characteristic value) is measured, the contact of the rotary contact  40  is switched between electrodes C and A and the electrical characteristic value (third characteristic value) is measured, the contact of the rotary contact  40  is then switched between electrodes D and A and the electrical characteristic value (first characteristic value) is measured, the contact of the rotary contact  40  is next switched between electrodes B and D and the electrical characteristic value (fifth characteristic value) is measured, the contact of the rotary contact  40  is further switched between electrodes A and B and the electrical characteristic value (fourth characteristic value) is measured, and next, the contact of the rotary contact  40  is switched between electrodes A and C and the electrical characteristic value (third characteristic value) is measured. Note that in this operation example, the fifth characteristic value and the third characteristic value are measured in an overlapping manner, but it is preferable to control the rotation angle of the rotary contact  40  so as not to overlap. Since the rotary contact  40  can switch contact to any two of the electrodes  13  in this manner, even if the number of electrodes  13  increases, six characteristic values (first to sixth characteristic values) can be measured with only one electric characteristic measurement instrument  16 . As a result, workpiece extraction detection can be executed with few restrictions. 
     According to the embodiments described above, by providing the hand  10  with at least three electrodes  13 , the gripping state of the workpiece can be detected. Furthermore, the number of workpieces extracted can be detected by measuring the electrical characteristics of an electric circuit formed by contact between any two of the electrodes  13  and the workpiece. Since the extraction of workpieces is detected by measuring the electrical characteristics, the workpiece is not limited to magnetic materials and it is sufficient that it be a conductive material. Furthermore, the extraction of workpieces can be detected even if the workpieces are in close contact with each other in a state where the outer shapes thereof are aligned. Thus, workpiece extraction detection (detection of the number of extractions, detection of the gripping state, etc.) can be executed with few restrictions. 
     Furthermore, since the electrode  13  protrudes from the suction pad  12 , the extraction of workpieces can be detected even with a Bernoulli-type hand which holds workpieces in a non-contact manner. Further, even if the workpiece has poor adhesion such as wrinkles or unevenness, the electrodes  13  can ascend in accordance with the shape of the workpiece, whereby workpiece extraction detection can be executed with few restrictions. 
     Further, since the rotary contact  40  can switch contact to any two of the electrodes  13 , even if the number of electrodes  13  increases, the electrical characteristic values between any of the electrodes can be measured with only one electric characteristic measurement instrument  16 . As a result, workpiece extraction detection can be executed with few restrictions. 
     The program executed by the processor described above and the program for executing the flowchart described above may be recorded and provided on a computer-readable non-transitory recording medium such as a CD-ROM, or be may wired or wirelessly distributed and provided from a server device on a WAN (wide area network) or LAN (local area network). 
     Though various embodiments have been described herein, it should be noted that the invention is not limited to the embodiments described above and various modifications can be made within the scope of the claims. 
     DESCRIPTION OF REFERENCE SIGNS 
     
         
           1  hand system 
           10  hand 
           11  palm 
           12  suction pad 
           12   a  nozzle 
           12   b  nozzle hole 
           12   c  suction surface 
           13  electrode 
           13   a  electrode tube 
           13   b  spring 
           13   c  locking member 
           14  electrical line 
           15  position deviation suppression pad 
           15   a  surface 
           16  electric characteristic measurement instrument 
           17  fluid regulator 
           20  transport device 
           30  controller 
           31  determination unit 
           32  transport control unit 
           40  rotary contact 
           40   a ,  40   b  terminal 
           41   a ,  41   b  terminal 
           42   a ,  42   b  terminal 
           50  mounting device 
         W workpiece