Patent Publication Number: US-2023145441-A1

Title: Pneumatic actuator control device

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This is the U.S. National Phase application of PCT/JP2021/015206, filed Apr. 12, 2021, which claims priority to Japanese Patent Application No. 2020-073677, filed Apr. 16, 2020, the disclosures of these applications being incorporated herein by reference in their entireties for all purposes. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to a pneumatic actuator controller. 
     BACKGROUND OF THE INVENTION 
     Air cylinders are often used as pneumatic actuators for the driving of air chucks, slide tables, and the like. When using an air cylinder, it is common to attach an auto switch to the air cylinder, which confirms whether the piston rod is in a protruding position or a return position (for example, Patent Literature 1 and Patent Literature 2). 
     The air cylinder 10 of Patent Literature 2 is configured such that a pressure sensor 20 is further arranged in an operation chamber 12 of a cylinder 11. Regarding this configuration, Patent Literature 2 describes “In S5, it is determined whether or not the detection signal of the pressure sensor 20 matches the setting characteristic of the working pressure. When the determination of S5 is yes, the process proceeds to S6, but when the determination of S5 is no, the process proceeds to S8. In S6, failure of the position switch 19 is determined, and thereafter, the operating position of the air cylinder 10 is determined based on the detection signal of the pressure sensor 20. Specifically, the operation of the air cylinder 10 is controlled in accordance with the operating position calculated based on the detection signal of the pressure sensor 20 from the setting characteristic of the operating pressure” (paragraph 0020). 
     Patent Literature 3 describes, regarding a vehicle automatic door opening/closing device using an air cylinder, that “based on the air pressure detected by the pressure sensor 18 when foreign matter is caught during the closing operation of the left door 3A and the right door 3B, or when foreign matter is drawn, during the opening operation, into the door pocket in which the left door 3A and the right door 3B are housed, the control unit 17 switches the air supply/exhaust direction of the air supply/exhaust switching valve 6 and switches the opening/closing operation of the left door 3A and the right door 3B” (paragraph 0020). 
     PATENT LITERATURE 
     
         
         [PTL 1] Japanese Unexamined Patent Publication (Kokai) No. 2012-060906 
         [PTL 2] Japanese Unexamined Patent Publication (Kokai) No. 2004-225767 
         [PTL 3] Japanese Unexamined Patent Publication (Kokai) No. 2019-138060 
       
    
     SUMMARY OF THE INVENTION 
     In a configuration in which an auto switch is used in the operation confirmation of an air cylinder, since it is necessary to install an auto switch for each air cylinder and perform wiring, the wiring becomes more complicated as the number of air cylinders in the system increases. Furthermore, assuming that the air chuck grips workpieces of different sizes, since the closed position of the air chuck, i.e., the operation end position of the air cylinder, will be different for each workpiece, it is practically impossible to detect all of the positions by installing an auto switch. 
     A pneumatic actuator controller which can avoid complication of wiring and the like that may occur when such an auto switch is used is desired. 
     An aspect of the present disclosure provides a pneumatic actuator controller, comprising a detector which is arranged in an air supply path from an air supply source to a solenoid valve or an air exhaust path from the solenoid valve and which detects a flow rate or pressure of air in the air supply path or a flow rate or pressure of air in the air exhaust path, and an operation state judgment unit configured to judge an operation state of a pneumatic actuator connected to the solenoid valve based on data indicating change in the flow rate or pressure of air in the air supply path or the flow rate or pressure of the air in the air exhaust path detected by the detector. 
     According to the configuration described above, complication of wiring and the like that may occur when an auto switch is used can be avoided. 
     The object, features, and advantages of the present invention and other objects, features, and advantages will be further clarified from detailed descriptions of typical embodiments of the present invention illustrated in the attached drawings. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG.  1    is a view showing the structure of an actuator control system comprising a pneumatic actuator controller according to an embodiment. 
         FIG.  2    is a functional block diagram of a controller. 
         FIG.  3    shows flow rate and pressure waveform data obtained by a flow sensor and pressure sensor attached in an air supply path when a piston rod of an air cylinder moves from a retracted position to a forwardmost position. 
         FIG.  4 A  is a view schematically illustrating a series of movements from a state where a piston rod of an air cylinder is in a retracted position to a forwardmost position along with  FIGS.  4 B to  4 D . 
         FIG.  4 B  is a view schematically illustrating a series of movements from a state where a piston rod of an air cylinder is in a retracted position to a forwardmost position along with  FIGS.  4 A,  4 C , and  4 D. 
         FIG.  4 C  is a view schematically illustrating a series of movements from a state where a piston rod of an air cylinder is in a retracted position to a forwardmost position along with  FIGS.  4 A,  4 B , and  4 D. 
         FIG.  4 D  is a view schematically illustrating a series of movements from a state where a piston rod of an air cylinder is in a retracted position to a forwardmost position along with  FIGS.  4 A to  4 C . 
         FIG.  5    shows flow rate and pressure waveform data obtained by a flow sensor and a pressure sensor attached in an air exhaust path when a piston rod of an air cylinder moves from a retracted position to a forwardmost position. 
         FIG.  6    is a flowchart showing an air cylinder control process in the case in which one air cylinder moves. 
         FIG.  7    is a view showing waveform data in the case in which a first of three air cylinders moves. 
         FIG.  8    is a view showing waveform data in the case in which a second of three air cylinders moves. 
         FIG.  9    is a view showing waveform data in the case in which a third of three air cylinders moves. 
         FIG.  10    is a view showing composite waveform data in the case in which three air cylinders move. 
         FIG.  11    is a flowchart showing an air cylinder control process in the case in which three air cylinders move. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION 
     Next, the embodiments of the present disclosure will be described with reference to the drawings. In the referenced drawings, identical constituent portions of functional portions are assigned the same reference sign. In order to facilitate understanding, the scales of the drawings have been appropriately changed. Furthermore, the aspects shown in the drawings are merely examples for carrying out the present invention, and the present invention is not limited to the illustrated aspects. 
       FIG.  1    is a view showing the structure of an actuator control system  100  comprising a pneumatic actuator controller  10  according to an embodiment. As shown in  FIG.  1   , the actuator control system  100  comprises three air cylinders  1  to  3 , solenoid valves  51  to  53  which perform the respective opening/closing control of air to be supplied to the air cylinders  1  to  3 , and a controller  10  which controls the solenoid valves  51  to  53 . The air cylinders  1  to  3  are double-acting air cylinders in the present embodiment. Each of the solenoid valves  51  to  53  is a four-way solenoid valve having, for example, one supply port, two cylinder ports, and one exhaust port. In  FIG.  1   , representatively, the supply port, two cylinder ports, and exhaust port of the solenoid valve  51  have been assigned the reference signs  51 P,  51 A,  51 B, and  51 E, respectively. The supply port of each of the solenoid valves  51  to  53  is commonly connected to an air supply path  81 , for example, formed of an air hose from an air supply source. The exhaust port of each of the solenoid valves  51  to  53  is commonly connected to an air exhaust path  91 , for example, formed of an air hose. Below, for convenience of explanation, the solenoid valves  51  to  53  may be collectively referred to as the solenoid valve  5 . 
     Each of the solenoid valves  51  to  53  is electrically connected to the controller  10 , and each of the solenoid valves  51  to  53  operates in accordance with operation commands from the controller. The types of air cylinders  1  to  3  and solenoid valves  51  to  53  shown here are exemplary, and other types of air cylinders (for example, single-acting air cylinders) and other types of solenoid valves (for example, three-way solenoid valves) may be used. 
     As shown in  FIG.  1   , a flow sensor  61  which detects the flow rate of air flowing in the air supply path  81  and a pressure sensor  62  which detects the pressure of air in the air supply path  81  are arranged in the air supply path  81  from the air supply source to the solenoid valve  5 . Furthermore, a flow sensor  71  which detects the flow rate of air flowing in the air exhaust path  91  and a pressure sensor  72  which detects the pressure of air in the air exhaust path  91  are arranged in the air exhaust path  91  which guides exhaust from the solenoid valve  5 . Note that though a configuration example of the case in which there are three air cylinders is illustrated in  FIG.  1   , the number of air cylinders may be 1, or may be a plurality of air cylinders other than three. 
     The controller  10  can control each of the solenoid valves  51  to  53  by transmitting electrical signals as operation commands to the solenoid valves  51  to  53 . Note that the controller  10  may have a structure as a general computer comprising a CPU, ROM, RAM, a storage device, operation units, a display unit, an input/output interface, a networking interface, etc. 
     The air cylinders  1  to  3  drive, for example, a gripping device (chuck) equipped on a robot device. In this case, the actuator control system  100  functions as a system which performs opening/closing control of the gripping device equipped on the robot device in accordance with commands from a host device (robot controller). 
     As shown in  FIG.  2   , the controller  10  comprises an operation state judgment unit  11  which judges the operation states of the air cylinders  1  to  3  based on any of the flow rate detected by the flow sensor  61 , the pressure detected by the pressure sensor  62 , the flow rate detected by the flow sensor  71 , and the pressure detected by the pressure sensor  72 , and a solenoid valve control unit  12  which executes control of the air cylinders  1  to  3  based on the operation states of the air cylinders  1  to  3  judged by the operation state judgment unit  11 . 
     Regarding the flow rate and pressure waveform data obtained by the flow sensor  61  and the pressure sensor  62  when the air cylinders move, as an example, the case in which only a single air cylinder  1  moves will be described with reference to  FIGS.  3  and  4 A to  4 D . Below, for ease of explanation, the direction in which the piston rod  1   a  (refer to  FIGS.  4 A to  4 D ) of the air cylinder advances and protrudes to the outside (the direction of arrow A in  FIG.  4 B ) is referred to as the advancing direction, and the direction in which the piston rod  1   a  retracts and enters the cylinder chamber is referred to as a retracting direction. 
       FIG.  3    shows flow rate and pressure waveform data obtained by the flow sensor  61  and the pressure sensor  62  when the piston rod  1   a  of the air cylinder  1  moves from the retracted position to the forwardmost position. In  FIG.  3   , the horizontal axis represents time and the vertical axis represents flow rate and pressure. In  FIG.  3   , the solid line graph  101  shows the transition of the flow rate detected by the flow sensor  61 , and the dashed line graph  102  shows the transition of the pressure detected by the pressure sensor  62 . 
       FIGS.  4 A to  4 D  schematically show a series of movements from the state in which the piston rod  1   a  of the air cylinder  1  is in the retracted position to the forwardmost position. In  FIGS.  4 A to  4 D , the portion indicated by reference sign  30  is the portion of the air supply source side (primary side). Reference sign  21  represents the air supply path (for example, an air hose) from the air supply source side to the solenoid valve  51 , and reference sign  22  represents the air supply path (for example, an air hose) from the solenoid valve  51  to the air cylinder  1 . Note that the flow sensor  61  and the pressure sensor  62  are arranged in the supply path  21 . Note that in  FIGS.  4 A to  4 D , the hatching shown in the portion  30  of the air supply source side, the supply path  21 , the supply path  22 , and the air cylinder  1  represents the air pressure according to concentration (the higher the concentration of the hatching (darker), the greater the air pressure). 
       FIG.  4 A  is a state before the start of the driving of the cylinder, and corresponds to a state before time t 0  in  FIG.  3   . In the state of  FIG.  4 A , the flow rate detected by the flow sensor  61  is zero, and the air pressure detected by the pressure sensor  62  is a high state. 
     At time t 0 , the solenoid valve  51  is driven, and the air cylinder  1  starts to move.  FIG.  4 B  corresponds to the state at this time. In the solenoid valve  51 , as the flow path from the air supply source side to the air cylinder  1  side is opened, the inflow of air into the cylinder chamber  1   c  of the air cylinder  1  starts. The cylinder chamber partitioned on the rear end side of the piston inside the air cylinder  1  is referred to as the cylinder chamber  1   c , and the cylinder chamber partitioned on the front end side of the piston is referred to as the cylinder chamber  1   d . When the inflow of air into the cylinder chamber  1   c  starts, the piston rod  1   a  starts to move forward. As shown in  FIG.  3   , as the inflow of air into the cylinder chamber  1   c  starts, the flow rate detected by the flow sensor  61  increases, and the pressure detected by the pressure sensor  62  decreases. 
     As shown in  FIG.  3   , the state in which the flow rate is increased and the pressure is decreased continues until the piston rod  1   a  moves to the front end. Finally, the piston rod  1   a  reaches the forwardmost position ( FIG.  4 C ). In  FIG.  3   , time t 1  is the timing when the piston rod  1   a  reaches the forwardmost position. As shown in  FIGS.  3  and  4 C , when the piston rod  1   a  reaches the forwardmost position, the flow rate begins to decrease and the pressure begins to increase. At time t 2 , the flow rate and pressure return to the states before time t 0 .  FIG.  4 D  shows the state of the air cylinder  1  after time t 2 . In the state of  FIG.  4 D , the pressure in the air cylinder  1  rises and the theoretical cylinder thrust is generated. 
     After the driving of the air cylinder  1  has started, the controller  10  (operation state judgment unit  11 ) can judge that the movement of the air cylinder  1  has ended by capturing the timing of the decrease in flow rate in the flow rate waveform or the timing of the increase in pressure in the pressure waveform. Note that though the detection of the end of the movement when the piston rod  1   a  advances has been described, the end of the movement when the piston rod  1   a  returns from the front end to the rear end can be determined by the same method. In this manner, the controller  10  (operation state judgment unit  11 ) can understand the operation state (position of the piston rod) of the air cylinder by analyzing the waveform data of the flow sensor  61  or the pressure sensor  62 . The controller  10  (solenoid valve control unit  12 ) can appropriately move to the execution of a subsequent operation command commanded by the host device under the condition that the end of the predetermined movement of the air cylinder is detected in this manner. 
     Note that though  FIGS.  4 C and  4 D  illustrate an example of the case in which the piston rod  1   a  is in a state in which it has reached the forwardmost position, for example, even in the case in which the position of the piston rod  1   a  of  FIGS.  4 C and  4 D  is a position in which an air chuck driven by the air cylinder  1  grips a workpiece, likewise, the end of movement (i.e., the completion of the movement for closing the chuck) can be judged. 
     According to the configuration described above, unlike the prior art, it is not necessary to arrange a sensor such as a so-called “auto switch” for each of the air cylinders in order to confirm the operation state of the air cylinders. Furthermore, even in a situation where the air chuck attempts to grip workpieces of different sizes, the end of the movement of the air cylinder (the completion of the movement for closing the chuck) can accurately be judged. 
       FIG.  5    shows flow rate and pressure waveform data obtained by the flow sensor  71  and the pressure sensor  72  attached in the air exhaust path  91  when the air cylinder  1  performs the series of movements shown in  FIGS.  4 A to  4 D . In  FIG.  5   , the solid line graph  141  shows the transition of the flow rate detected by the flow sensor  71 , and the dashed line graph  142  shows the transition of the pressure detected by the pressure sensor  72 . When the air cylinder  1  performs the movement shown in  FIGS.  4 A to  4 D , the cylinder chamber  1   d  is connected to the air exhaust path  91  by the movement settings for the solenoid valve  51 . 
     Regarding the flow rate detected by the flow sensor  71 , in the same manner as the case of the flow rate detected by the flow sensor  61  shown in  FIG.  3   , as the movement of the piston rod  1   a  to the front end side starts, the flow rate begins to increase (time t 0 ). Regarding the pressure detected by the pressure sensor  72  at this time, the pressure changes from zero as the movement of the piston rod  1   a  to the front end side starts. While the piston rod  1   a  moves from the rear end to the front end, the state in which the flow rate is increased and the pressure is increased continues. 
     Eventually, the piston rod  1   a  reaches the forwardmost position ( FIG.  4 C ). In  FIG.  5   , time t 1  is the timing when the piston rod  1   a  reaches the forwardmost position. As shown in  FIG.  5   , when the piston rod  1   a  reaches the forwardmost position, the flow rate starts to decrease and the pressure also starts to decrease. Then, at time t 2 , the flow rate and pressure return to the states before time t 0 . 
     Even in the case in which the controller  10  (operation state judgment unit  11 ) uses the flow sensor  71  or the pressure sensor  72  arranged in the air exhaust path  91  in this manner, by capturing the timing of the fall of the flow rate waveform or the pressure waveform, the end of the predetermined movement of the air cylinder  1  can be determined. In other words, by using either the flow sensor  71  or the pressure sensor  72  arranged in the air exhaust path  91 , the same effect as the case in which either the flow sensor  61  or the pressure sensor  62  arranged in the air supply path  81  is used can be obtained. 
     Two examples of embodiments of air cylinder control (air cylinder control methods) by the controller  10  will be described below. The first embodiment ( FIG.  6   ) is an operation example in the case in which there is one air cylinder, and the second embodiment ( FIG.  11   ) is an operation example in the case in which three air cylinders are controlled in parallel. 
       FIG.  6    is a flowchart showing movement when one air cylinder is the target of control by the controller  10 . The control target is the solenoid valve  51  (air cylinder  1 ). The air cylinder control process of  FIG.  6    (and  FIG.  11   ) is executed under the control of the CPU of the controller  10 . To facilitate understanding,  FIG.  6    shows the operation state of the air cylinder and the trend of the detected waveform together with the control flow. 
     As shown in  FIG.  6   , first, the controller  10  turns on the solenoid valve  51  to open an air supply path to the air cylinder  1  (step S 1 ). The controller  10  (operation state judgment unit  11 ) then monitors the waveform representing the air flow rate and the waveform representing the change in pressure obtained by the flow sensor  61  and the pressure sensor  62 . As the solenoid valve  51  is turned on, the air cylinder  1  starts to move (box K 1 ), the air flowing into the air cylinder  1  increases, and the pressure detected by the pressure sensor  62  decreases (box K 2 ). 
     The piston rod  1   a  moves to the end of the stroke, the pressure in the air cylinder  1  rises, the theoretical cylinder thrust is generated, and when the movement of the air cylinder  1  ends (box K 3 ), the inflow of air into the air cylinder  1  is stopped and the flow rate drops to zero, whereby the pressure returns to the original high state. In step S 2 , the controller  10  (operation state judgment unit  11 ) detects that the piston rod  1   a  of the air cylinder  1  has reached the stroke end (the movement of the air cylinder  1  is complete) by monitoring the waveform of the inflow amount and the waveform of the pressure. The monitoring in step S 2  is continued until a change in which the flow rate drops to zero and the pressure returns to the original level is detected (S 2 : NG). 
     When the change wherein the flow rate drops to zero and the pressure returns to the original level is detected (S 2 : OK), the controller  10  understands that the movement of the air cylinder  1  is complete, i.e., the piston rod had reached the stroke end and the cylinder thrust has been generated, and turns off the solenoid valve  51 . The solenoid valve  51  may remain on until the next movement. As a result, the process ends. 
     According to the first embodiment, even in a situation where workpieces of different sizes are gripped by an air chuck, the operation state of the air cylinder can be appropriately determined with a simple structure. By understanding the position of the piston rod  1   a  of the air cylinder  1  in this manner, the controller  10  can accurately move to the control of a subsequent operation command. 
     Next, the second embodiment of air cylinder control by the controller  10  will be described. In the second embodiment, the controller  10  moves three air cylinders  1  to  3  in parallel. It will be assumed that the air cylinders  1  to  3  have the same cylinder chamber inner diameters, and the total lengths (maximum strokes) thereof have the following relationship: 
       Air cylinder 2&gt;Air cylinder 1&gt;Air cylinder 3 
     When the air cylinders  1  to  3  are moved in parallel, the flow sensor  61  and the pressure sensor  62  provide waveform data obtained by compositing the waveform data of the cases in which the air cylinders  1  to  3  are individually moved (the waveform data graph at the bottom of  FIG.  10   ). The operation state judgment unit  11  determines the operation state of each of the air cylinders  1  to  3  by analyzing this composite waveform data. Below, the waveform data detected by the flow sensor  61  and the pressure sensor  62  when each of the air cylinders  1  to  3  is moved individually will be described with reference to  FIGS.  7  to  9   , and it will be described how the operation state judgment unit  11  judges the operation state of each of the air cylinders  1  to  3  from the composite waveform data. In the present embodiment, the air cylinders  1  to  3  are moved in the order of air cylinders  1  to  3 . 
       FIG.  7    shows the waveform data detected by the flow sensor  61  and the pressure sensor  62  when the air cylinder  1  independently performs a round-trip movement,  FIG.  8    shows the waveform data detected by the flow sensor  61  and the pressure sensor  62  when the air cylinder  2  independently performs a round-trip movement, and  FIG.  9    shows waveform data detected by the flow sensor  61  and the pressure sensor  62  when the air cylinder  3  independently performs a round-trip movement. For convenience of explanation, on the right side of each of  FIGS.  7  to  9   , a state in which the piston rod ( 1   a ,  2   a ,  3   a ) of the air cylinder ( 1 ,  2 ,  3 ) is in the rear end position (upper side), and a state in which the piston rod ( 1   a ,  2   a ,  3   a ) of the air cylinder ( 1 ,  2 ,  3 ) is in the forwardmost position (lower side) are shown. 
     In  FIG.  7   , graphs  111  and  112  respectively show the waveform data of the flow rate detected by the flow sensor  61  and the waveform data of the pressure detected by the pressure sensor  62  when the air cylinder  1  is moved. In  FIG.  7   , the movement of the air cylinder  1  is started at time t 11  from the state in which the piston rod  1   a  is retracted to the rear end. As a result, at time t 11 , the flow rate begins to increase and the pressure begins to decrease. 
     The state in which the flow rate increases and the pressure decreases continues until the piston rod  1   a  reaches the front end at time t 12 . When the piston rod  1   a  reaches the front end and the forward movement of the piston rod  1   a  ends, the flow rate decreases, the pressure increases, and the original state is restored. The controller  10  starts driving the air cylinder  1  in the retracting direction at time t 13 . Along with this, the flow rate increases and the pressure begins to decrease. The state in which the flow rate increases and the pressure decreases continues until the piston rod  1   a  returns to the rear end position. At time t 14  when the piston rod  1   a  returns to the rear end position, the flow rate decreases, the pressure increases, and the original state is restored. 
     In the waveform data of  FIG.  7   , when the period T 101  during which the piston rod  1   a  moves forward from the rear end position to the forwardmost position and the period T 102  during which the piston rod  1   a  retracts from the forwardmost position to the rear end position are compared with each other, it can be understood that the period T 101  is longer. This is because the lengths of the period T 101  and the period T 102  correspond to the air consumption amount (total amount of flowing air), and in the case of a movement in which the piston rod  1   a  retracts, the amount of air consumption is smaller than that in the case of the piston rod  1   a  moving forward by the amount corresponding to the volume of the piston rod  1   a.    
     In  FIG.  8   , graphs  211  and  212  respectively show the waveform data of the flow rate detected by the flow sensor  61  and the waveform data of the pressure detected by the pressure sensor  62  when the air cylinder  2  is moved. In the same manner as the case of  FIG.  7   , in  FIG.  8   , time t 21  is the time when the piston rod  2   a  starts moving forward from the rear end position. Time t 22  is the time when the piston rod  2   a  reaches the front end. Time t 23  is the time when the piston rod  2   a  starts moving from the front end to the rear side. Time t 24  is the time when the piston rod  2   a  reaches the rear end. As described above, since the air consumption amount when the piston rod  2   a  moves from the rear end to the front end is greater than the air consumption amount when the piston rod  2   a  moves from the front end to the rear end, the period T 111  from time t 21  to time t 22  is longer than the period T 112  from time t 23  to time t 24 . 
     In  FIG.  9   , graphs  311  and  312  respectively show the waveform data of the flow rate detected by the flow sensor  61  and the waveform data of the pressure detected by the pressure sensor  62  when the air cylinder  3  is moved. In the same manner as the case of  FIG.  7   , in  FIG.  9   , time t 31  is the time when the piston rod  3   a  starts moving forward from the rear end position. Time t 32  is the time when the piston rod  3   a  reaches the front end. Time t 33  is the time when the piston rod  3   a  starts moving from the front end to the rear side. Time t 34  is the time when the piston rod  3   a  reaches the rear end. As described above, since the air consumption amount when the piston rod  3   a  moves from the rear end to the front end is greater than the air consumption amount when the piston rod  3   a  moves from the front end to the rear end, the period T 121  from time t 31  to time t 32  is longer than the period T 122  from time t 33  to time t 34 . 
     The operation for understanding the position of each of the air cylinders  1  to  3  by waveform analysis of the composite waveform will be described below. When the air cylinders  1  to  3  perform the movements of the operation waveforms shown in  FIGS.  7  to  9    in parallel, the waveform data obtained by compositing graphs  111 ,  211 , and  311  of  FIGS.  7  to  9    is obtained as output of the flow sensor  61 , and the waveform obtained by compositing graphs  112 ,  212  and  312  is obtained as the output of the pressure sensor  62 . Graph  411  of the composite waveform of the flow rate detected by the flow sensor  61  and graph  412  of the composite waveform of the pressure detected by the pressure sensor  62  are shown at the bottom of  FIG.  10   . Furthermore, in  FIG.  10   , in order to facilitate understanding of graphs  411  and  412 , each graph of  FIGS.  7  to  9    is reprinted aligned with graphs  411  and  412  on the time axis. 
       FIG.  11    is a flowchart showing control flow in the second embodiment of air cylinder control. The control flow of  FIG.  11    will be described while referring to the waveform data of  FIG.  10   . Note that for ease of description, in each processing step in the flowchart of  FIG.  11   , the solenoid valves  51  to  53  will be referred to as solenoid valves  1  to  3 , respectively. First, the controller  10  turns on the solenoid valve  51  at time t 11  (step S 101 ). The controller  10  monitors the waveform data detected by the flow sensor  61  and the pressure sensor  62  (step S 102 ). The controller  10  waits for the waveform data to change and the start of the movement of the air cylinder  1  to be confirmed (step S 102 : NG). As the solenoid valve  51  is turned on, the air cylinder  1  begins to move (box K 101 ), the flow rate increases, and the pressure decreases (box K 102 ). When the start of movement is confirmed by the change of the waveform data (S 102 : OK), the process proceeds to the next step S 103 . At this stage, the end of the movement of the air cylinder does not occur. 
     In step S 103 , the controller  10  turns on the solenoid valve  52  at time t 21 . The controller  10  monitors the waveform data detected by the flow sensor  61  and the pressure sensor  62  (step S 104 ). The controller  10  waits for the waveform data to change and the start of the movement of the air cylinder  1  to be confirmed (step S 104 : NG). As the solenoid valve  52  is turned on, the air cylinder  2  beings to move (box K 103 ), the flow rate increases, and the pressure decreases (box K 104 ). When the start of movement is confirmed by the change of the waveform data (S 104 : OK), the process proceeds to the next step S 105 . At this stage, the end of the movement of the air cylinder does not occur. 
     In step S 105 , the controller  10  turns on the solenoid valve  53  at time t 31 . The controller  10  monitors the waveform data detected by the flow sensor  61  and the pressure sensor  62  (step S 106 ). The controller  10  waits for the end of the movement of any of the air cylinders (S 106 : NG). As the solenoid valve  53  is turned on, the air cylinder  3  begins to move (box K 105 ), the flow rate increases, and the pressure decreases (box K 106 ). 
     At time t 12  after the start of the movement of the air cylinder  3 , the movement of the air cylinder  1  ends (box K 107 ), a change in which the flow rate decreases and the pressure increases occurs (box K 108 ). The controller  10  (operation state judgment unit  11 ) captures the change in the falling edge in this case in the flow rate waveform (or the change in the rising edge in this case in the pressure waveform) (the portion indicated by reference sign F 1 ). Specifically, the operation state judgment unit  11  captures an edge-like change in the flow rate waveform or the pressure waveform. The portion where the flow rate waveform falls or the portion where the pressure waveform rises is the timing when the movement of any of the air cylinders  1  to  3  is complete. The controller  10  specifies, for example, the air cylinder for which the movement is complete by the following operation. 
     The controller  10  retains a table in which the consumption amount of air when, for example, each of the air cylinders  1  to  3  is moved from the rear end position to the forwardmost position is stored. For example, the reference values retained in the table as the air consumption amount when each of the air cylinders  1  to  3  moves from the rear end position to the forwardmost position are as follows. 
     Air cylinder  1 : V 1  (liters) 
     Air cylinder  2 : V 2  (liters) 
     Air cylinder  3 : V 3  (liters) 
     The controller  10  acquires the flow rate when each air cylinder moves by, for example, detecting the height of the rise of the flow rate immediately after the start of movement. Alternatively, the flow rate of each air cylinder may be stored in advance by test operation. As an example, the flow rate detected for the air cylinder  1  is C 1  (L/min). By multiplying the elapsed time from time t 11  when the movement of the air cylinder  1  begins to the time t 12  when the falling edge of the flow rate waveform is detected by the flow rate C 1  (formula (1) below), the amount of air inflow for the air cylinder  1  can be determined. 
       (Air inflow of air cylinder 1)= C 1×(elapsed time)  (1)
 
     When the air inflow amount of the air cylinder  1  determined in this manner substantially matches the air consumption amount V 1  in the forward movement of the air cylinder  1  stored in advance, it can be specified that the air cylinder for which the movement is complete is the air cylinder  1 . In this case, the air inflow amount from the time t 11  to the time t 12  is calculated in the same manner for the air cylinders  2  and  3 , and comparison with V 2  and V 3  in the forward move of the air cylinders  2  and  3  stored in advance is also performed. The air inflow amount from the time t 11  to the time t 12  calculated for the air cylinders  2  and  3  does not match the air consumption amounts V 2  and V 3  for the air cylinders  2  and  3 . 
     For the falling edges of the flow rate waveform detected at time t 32  and time t 22 , the air cylinder for which the movement has ended is specified in the same manner. 
     When the end of the movement of the air cylinder  1  is confirmed in this manner (S 106 : OK), the controller  10  turns off the solenoid valve  51  (step S 107 ). The controller  10  then monitors the waveform data detected by the flow sensor  61  and the pressure sensor  62  (step S 108 ). The controller  10  waits for the end of the movement of any of the air cylinders (S 108 : NG). 
     At time t 32 , the movement of the air cylinder  3  ends (box K 109 ), and a change in which the flow rate further decreases and the pressure further increases occurs (box K 110 ). The controller  10  captures the change in the falling edge in this case of the flow rate waveform (or the change in the rising edge in this case of the pressure waveform) (the portion indicated by reference sign F 2 ). The portion where the flow rate waveform falls or the portion where the pressure waveform rises is the timing when the movement of any of the air cylinders  1  to  3  has completed. The controller  10  specifies the air cylinder for which the movement has completed by the same method as the method described above for specifying the end of the movement of the air cylinder  1 . Since the amount of air flowing into the air cylinder  3  between the time t 31  and the time t 32  is substantially the same as the air consumption amount V 3  of the air cylinder  3 , it can be specified that the air cylinder for which the movement has completed is the air cylinder  3 . 
     When the end of movement of the air cylinder  3  is confirmed in this manner (S 108 : OK), the controller  10  turns off the solenoid valve  53  (step S 109 ). The controller  10  then monitors the waveform data detected by the flow sensor  61  and the pressure sensor  62  (step S 110 ). The controller  10  waits for the end of the movement of any of the air cylinders (S 110 : NG). 
     At time t 22 , the movement of the air cylinder  2  ends (box K 111 ), the flow rate becomes zero, and the pressure returns to the original state (box K 112 ). The controller  10  captures the change in the falling edge in this case of the flow rate waveform (or the change in the rising edge in this case of the pressure waveform) (the portion indicated by the symbol F 3 ). The portion where the flow rate waveform falls or the portion where the pressure waveform rises is the timing when the movement of any of the air cylinders  1  to  3  is complete. The controller  10  specifies the air cylinder for which the movement has completed by the same method as the method described above for specifying the end of the movement of the air cylinder  1 . Since the amount of air flowing into the air cylinder  2  between the time t 21  and the time t 22  is substantially the same as the air consumption amount V 2  of the air cylinder  2 , it can be specified that the air cylinder for which the move has completed is the air cylinder  2 . When the end of movement of the air cylinder  2  is confirmed in this manner (S 110 : OK), the controller  10  turns off the solenoid valve  52  (step S 111 ). 
     According to the second embodiment, by configuring the sensor (detector) arranged on the primary side (air supply source side) of the solenoid valve to detect the air flow rate and pressure, even when a plurality of air cylinders are connected to the secondary side of the solenoid valve, the operation state of each air cylinder can be appropriately determined without incurring complication of wiring that occurs when auto switches are attached to the air cylinders. 
     Note that though the end of movement of each air cylinder is determined using the flow sensor  61  or pressure sensor  62  arranged in the air supply path in the second embodiment described above, the end of the movement of each air cylinder can likewise be determined using the flow sensor  71  or pressure sensor  72  arranged in the air exhaust path. 
     The operation state judgment unit  11  of the controller  10  may be configured to detect that an abnormality has occurred in, for example, the air hose forming the air supply path  81  by analyzing the operation waveform of the flow sensor  61  and/or the pressure sensor  62 . Examples of operations for detecting abnormality in the air supply path  81  will be described below. Operation example 1 and operation example 2 are examples of detecting that a defect (hole, etc.) has occurred in the air supply path  81  (air hose), and operation example 3 is an example of detecting a state in which the air supply path  81  (air hose) has become kinked, making it difficult for air to flow. 
     (Operation example 1) For example, the normal air consumption amount when the air cylinder  1  moves from the rear end position to the forwardmost position is defined as V 1  (liter) and the operation time is defined as T 101  (seconds). The operation state judgment unit  11  analyzes the waveform of the air flow rate after the actuator control system  100  has operated for some time, and using the above-mentioned formula (1) or the like, acquires the consumption amount (inflow amount) of air and operation time when the air cylinder  1  moves from the rear end position to the forwardmost position. Further, when the consumption amount of air acquired in this manner exceeds V 1  (liter) or when the operation time exceeds T 101  (seconds), the operation state judgment unit  11  judges that a defect has occurred in the air supply path  81  since the air consumption amount has increased or air inflow takes more time as compared to normal operation. 
     (Operation example 2) It is considered that when a defect has occurred in the air supply path  81 , the rate of change of the rising edge and falling edge of the pressure fluctuation waveform detected by the pressure sensor  62  becomes blunt. The operation state judgment unit  11  can judge that a defect has occurred in the air supply path  81  when the rise or rate of change of the rising edge of the pressure waveform detected by the pressure sensor  62  is slower than in the normal state. 
     (Operation example 3) It will be assumed that the air hose forming the air supply path  81  is kinked, making it difficult for air to flow. In this case, since the air flow rate decreases as a whole, the air consumption amount is equal to the normal consumption amount V 1 , but the operation time is longer than the normal operation time T 101 . Thus, when such a situation occurs, the operation state judgment unit  11  can judge that the air hose is kinked, whereby air inflow is difficult. 
     According to the present embodiment as described above, by configuring the sensor (detector) arranged on the primary side (air supply source side) of the solenoid valve to detect the air flow rate and pressure, even when a plurality of air cylinders are connected to the solenoid valve, the operation state (position) of each air cylinder can properly be determined without causing complication of wiring, as in the case in which auto switches are used. Furthermore, even in a situation where workpieces of different sizes are gripped by an air chuck, the operation states of the air cylinders can be appropriately determined with a simple structure. 
     Specifically, according to the embodiments described above, complication of wiring and the like that may occur when an auto switch is used can be avoided. 
     Though the present invention has been described above using typical embodiments, a person skilled in the art could understand that modification and various other changes, omissions, and additions can be made to the embodiments described above without deviation from the scope of the present invention. 
     In the embodiments described above, as described in, for example, the flowchart of  FIG.  6   , the controller  10  detects the falling edge of the time fluctuation waveform of the flow rate, determines that the movement of the air cylinder has ended, and then transmits a subsequent operation command. From the viewpoint of shortening the cycle time in the control of the air cylinders, the controller  10  (solenoid valve control unit) may determine the total amount of air flowing into the air cylinder (or the total amount of air discharged from the air cylinder) after the predetermined movement of the air cylinder has started by analyzing the flow rate waveform, and may transmit a subsequent operation command to the solenoid valve on the condition that the total amount of the air has reached a predetermined ratio (for example, 90%) with respect to a reference value (for example, V 1  described above) stored in advance as a value representing the consumption amount of the air consumed by the air cylinder when the predetermined movement is performed. 
     The functional blocks of the controller  10  shown in  FIG.  2    may be realized by the CPU of the controller  10  executing various software stored in the storage device, or alternatively, may be realized by a hardware-based configuration such as an ASIC (application specific IC). 
     The program for executing the air cylinder control process of the embodiments described above can be recorded on various computer-readable recording media (for example, semiconductor memory such as ROM, EEPROM, and flash memory, magnetic recording medium, or an optical disk such as a CD-ROM or DVD-ROM). 
     DESCRIPTION OF REFERENCE SIGNS 
     
         
           1 ,  2 ,  3  air cylinder 
           1   a ,  2   a ,  3   a  piston rod 
           5  solenoid valve 
           10  controller 
           11  operation state judgment unit 
           12  solenoid valve control unit 
           51 ,  52 ,  53  solenoid valve 
           61 ,  71  flow sensor 
           62 ,  72  pressure sensor 
           81  air supply path 
           91  air exhaust path 
           100  actuator control system