Patent Publication Number: US-2021164499-A1

Title: Cylinder device

Description:
TECHNICAL FIELD 
     The present invention relates to a cylinder device including detection valves configured to detect the operational state of a piston. 
     BACKGROUND ART 
     Known examples of such a cylinder device include a device described in Patent Literature 1 specified below. 
     The known device is structured as follows. 
     Detection valves, which are configured to detect the operational state of a force multiplier provided in a cylinder device, are provided to a housing of the cylinder device. The two detection valves are provided in a lower end portion of the housing. For each of the detection valves, an air supply passage is provided. Namely, first and second air supply passages are respectively provided for the detection valves. 
     CITATION LIST 
     Patent Literature 
     Patent Literature 1: Japanese Unexamined Patent Publication No. 2017-15237 
     SUMMARY OF INVENTION 
     Technical Problem 
     The above-described known device has the following disadvantage. In the known device, the air supply passages are provided to the housing so as to correspond to the respective detection valves. Due to this, two (a plurality of) air supply ports have to be provided onto the housing. Furthermore, in order to detect the operational state of the force multiplier with the two detection valves, a pressure switch has to be provided for each air supply passage. 
     An object of the present invention is to provide a cylinder device arranged to detect the operational state of a piston by providing detection valves to a housing and configured so that the number of air supply ports can be reduced. 
     Solution to Problem 
     In order to achieve the above object, in the present invention, a cylinder device is structured as follows, as shown in  FIG. 1  to  FIG. 19B , for example. 
     A cylinder device of an aspect of the present invention includes: a housing  1 ; a piston  5 ,  59 ,  150  inserted in the housing  1 , the piston  5 ,  59 ,  150  being configured to move in an axial direction to a lock side and to a release side; a plurality of detection valves  12  and  13 ,  64  and  65 ,  121  and  122  provided to the housing  1 , the detection valves  12  and  13 ,  64  and  65 ,  121  and  122  being configured to detect an operational state of the piston  5 ,  59 ,  150 ; and at least one air passage  14  and  15 ,  66 ,  125  and  126  provided to the housing  1 , the air passage  14  and  15 ,  66 ,  125  and  126  communicatively connecting the detection valves  12  and  13 ,  64  and  65 ,  121  and  122  to each other in series. One or some of the detection valves  12  and  13 ,  64  and  65 ,  121  and  122  are each configured as a throttle detection valve  13 ,  65 ,  122  including a throttle passage  56   a ,  106 ,  107   a ,  149 . 
     The cylinder device of the above aspect of the present invention provides the following functions and effects. The detection valves are communicatively connected to each other in series by the air passage. This makes it possible to supply air to the detection valves through a common line. As a result, the number of air supply ports can be reduced. Furthermore, because one or some of the detection valves are each configured as the throttle detection valve, different operational states of the piston can be discriminated based on the difference in air pressure. This makes it also possible to reduce the number of pressure switches.  
     It is preferable that the cylinder device of the above aspect of the present invention further includes the following features. 
     The throttle detection valve  13  includes: a valve element  49  movably inserted in a valve chamber  48  provided in the housing  1 , the valve element  49  being biased by a biasing means  55  housed in the valve chamber  48 ; and a valve seat  54   a  facing a valve surface  53   a  of the valve element  49 , and the throttle passage  56   a  is provided at a central portion of an end portion of the valve element  49 , the end portion being opposite from a rod portion  50 . This makes it easy to produce the throttle detection valve. 
     Furthermore, it is preferable to arrange the cylinder device such that the valve element  49  includes: a valve element body  52 , at a first end portion of which the rod portion  50  is provided; and a throttle member  56  fixed to a central portion of a second end portion of the valve element body  52 , the second end portion being opposite from the rod portion  50 , the throttle member  56  having a hole  56   a  functioning as the throttle passage. 
     In this arrangement, the throttle member is a separate element. This makes it possible to conduct a test for pressure drop properties of the throttle passage on the throttle passage independently from other elements. 
     It is preferable that the cylinder device of the above aspect of the present invention further includes the following features. 
     The throttle detection valve  57  includes: a valve element  49  movably inserted in a valve chamber  48  provided in the housing  1 , the valve element  49  being biased by a biasing means  55  housed in the valve chamber  48 ; and a valve seat  54   a  facing a valve surface  53   a  of the valve element  49 , and the valve element  49  has a hole  58  functioning as the throttle passage; or a groove  70  functioning as the throttle passage is provided on the valve surface  53   a  or on the valve seat  54   a . This makes it easy to produce the throttle detection valve. 
     It is preferable that the cylinder device of the above aspect of the present invention further includes the following feature. 
     The detection valves  64  and  65  are provided in a lower end portion of the housing  1 . This allows the cylinder device to be made compact in size. 
     It is preferable that the cylinder device of the above aspect of the present invention further includes the following features. 
     At least one of the detection valves  12  and  13 ,  64  and  65 ,  121  and  122  is closed when the operational state of the piston  5 ,  59 ,  150  is a lock state, and at least one of the detection valves  12  and  13 ,  64  and  65 ,  121  and  122  is closed when the operational state is a release state. This makes the usage of air smaller, and therefore makes the cylinder device advantageous in terms of saving energy. 
     Advantageous Effects of Invention 
     According to embodiments of the present invention, it is possible to provide a cylinder device arranged to detect the operational state of a piston by providing detection valves to a housing, and configured so that the number of air supply ports can be reduced. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a first embodiment of the present invention, and is an elevational view in section of a cylinder device in a release state. 
         FIG. 2  is an elevational view in section of the cylinder device which is in the course of transition from the release state to a lock state. 
         FIG. 3  is an elevational view in section of the cylinder device in the lock state. 
         FIG. 4A  is an enlarged view of a part A in  FIG. 1 . 
         FIG. 4B  is an enlarged view of a part C in  FIG. 3 . 
         FIG. 5A  is an enlarged view of a part B in  FIG. 1 . 
         FIG. 5B  is an enlarged view of a part D in  FIG. 3 . 
         FIG. 6A  is a diagram illustrating a modification of a second detection valve (throttle detection valve) and corresponding to  FIG. 5A . 
         FIG. 6B  is a diagram illustrating the modification of the second detection valve (throttle detection valve) and corresponding to  FIG. 5B . 
         FIG. 7  shows a second embodiment of the present invention, and is an elevational view in section of a cylinder device in the release state. 
         FIG. 8  is an elevational view in section of the cylinder device which is in the course of transition from the release state to the lock state. 
         FIG. 9  is an elevational view in section of the cylinder device in the lock state. 
         FIG. 10  is an enlarged view of a part E in  FIG. 7 . 
         FIG. 11  is an enlarged view of a part F in  FIG. 8 . 
         FIG. 12  is an enlarged view of a part G in  FIG. 9 . 
         FIG. 13A  is a diagram illustrating another modification of the modification of the second detection valve (throttle detection valve) shown in  FIGS. 6A and 6B , and corresponding to  FIG. 5A . 
         FIG. 13B  is a diagram illustrating that another modification of the modification of the second detection valve (throttle detection valve) shown in  FIGS. 6A and 6B , and corresponding to  FIG. 5A . 
         FIG. 14  is a diagram illustrating a throttle detection valve of a modification in which a throttle passage is provided outside, and corresponding to  FIG. 1   
         FIG. 15  shows a third embodiment of the present invention, and is an elevational view in section of a cylinder device in the release state. 
         FIG. 16  is an elevational view in section of the cylinder device which is in the course of transition from the release state to the lock state. 
         FIG. 17  is an elevational view in section of the cylinder device in the lock state. 
         FIG. 18A  is an enlarged view of a part H in  FIG. 15 . 
         FIG. 18B  is an enlarged view of a part J in  FIG. 17 . 
         FIG. 19A  is an enlarged view of a part I in  FIG. 15 . 
         FIG. 19B  is an enlarged view of a part K in  FIG. 17 . 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
       FIG. 1  to  FIG. 5B  show a first embodiment of the present invention. This embodiment deals with a case in which the cylinder device of the present invention is applied to a link clamp, by way of example. The structure of a cylinder device of the first embodiment will be described with reference to  FIG. 1  to  FIG. 5B . 
     A housing  1  is attached to a stationary stand T such as a table. The housing  1  includes: a housing main body  2 ; and a lower end wall  3  fixed to a lower end portion of the housing main body  2 . A cylinder hole  4  is provided inside the housing main body  2 . 
     A piston  5  is hermetically inserted in the cylinder hole  4  so as to be movable in an up-down direction. The piston  5  has: a piston main body  6 ; and an output rod  7  extending from the piston main body  6 . 
     A left end portion of a clamp arm  8  is rotatably connected to an upper end portion of the output rod  7 . A pivot portion  2   b  is provided to protrude upward from an upper right portion of the housing main body  2 . A lower end portion of a link member  9  is rotatably connected to an upper end portion of the pivot portion  2   b . An intermediate portion of the clamp arm  8  in its longitudinal direction is rotatably connected to an upper end portion of the link member  9 . 
     A lock chamber  10  is provided below the piston main body  6 , and a release chamber  11  is provided above the piston main body  6 . Pressurized oil functioning as pressure fluid for locking is supplied to and discharged from the lock chamber  10 . Pressurized oil functioning as pressure fluid for releasing is supplied to and discharged from the release chamber  11 . Supply and discharge passages of pressurized oil for the lock chamber  10  and for the release chamber  11  are not illustrated. 
     A first detection valve  12  and a second detection valve  13 , which are configured to detect the operational state of the piston  5 , are respectively provided above a side wall of the housing main body  2  and at a central portion of the lower end wall  3 . An air passage  14  and an air passage  15 , which communicatively connect the first detection valve  12  and the second detection valve  13  to each other in series, are respectively provided in the side wall of the housing main body  2  and in the lower end wall  3 . 
     An air supply passage  16 , through which air (compressed air) functioning as fluid for detection is supplied to the detection valves  12  and  13  in this order, is provided in the side wall of the housing main body  2 . An air supply port  16   a  of the air supply passage  16  is communicatively connected to an air supply passage  17  provided in the stationary stand T. An air discharge passage  18 , through which air having been supplied to the detection valves  12  and  13  from the air supply passage  17  is discharged, is provided in the lower end wall  3 . An air discharge port  18   a  of the air discharge passage  18  is communicatively connected to an air discharge passage  19  provided in the stationary stand T. 
     The first detection valve  12  is structured as follows, as shown in  FIG. 4A  and  FIG. 4B .  
     A first attachment hole  21  is provided laterally above the side wall of the housing main body  2 . The first attachment hole  21  includes: a large-diameter hole  22  with an internal thread portion  22   a ; a middle-diameter hole  23 ; and a small-diameter hole  24 , which are provided in this order from a radially outside of the housing main body  2 . An annular pressing member  26  is fixed to a step portion  25  between the internal thread portion  22   a  and the middle-diameter hole  23  by a first valve case  27  screwed to the internal thread portion  22   a . A valve chamber  28  is provided inside the first valve case  27 , and the air supply passage  16  is communicatively connected to the valve chamber  28 . A first valve element  29  is inserted in the valve chamber  28 . A rod portion  30  of the first valve element  29  is movably inserted in the middle-diameter hole  23  via a sealing member  31 . An engagement ball  32  functioning as an operation portion configured to push a leading end of the rod portion  30  is inserted in the small-diameter hole  24 . The first valve element  29  includes a valve element body  33  having a flange portion  34 . A surface of the flange portion  34 , which is opposite from the rod portion  30 , is a valve surface  34   a . An annular sealing member  35  functioning as a valve seat member is fitted inside the first valve case  27 . The air passage  14  is communicatively connected to the valve chamber  28 . A compression spring  36 , functioning as a biasing means and attached between a bottom surface of the first valve case  27  and the valve element body  33 , biases the first valve element  29  in a direction in which the valve surface  34   a  moves away from a valve seat  35   a  of the sealing member  35 . 
     The second detection valve  13  is structured as follows, as shown in  FIG. 5A  and  FIG. 5B . 
     A second attachment hole  41  is provided in the up-down direction at the central portion of the lower end wall  3  of the housing  1 . The second attachment hole  41  includes: a large-diameter hole  42  with an internal thread portion  42   a ; a middle-diameter hole  43 ; and a small-diameter hole  44 , which are provided in this order from a bottom side of the lower end wall  3 . An annular pressing member  46  is fixed to a step portion  45  between the internal thread portion  42   a  and the middle-diameter hole  43  by a second valve case  47  screwed to the internal thread portion  42   a . A valve chamber  48  is provided inside the second valve case  47 , and the air passage  15  is communicatively connected to the valve chamber  48 . A second valve element  49  is inserted in the valve chamber  48 . A rod portion  50  of the second valve element  49  is movably inserted in the middle-diameter hole  43  via a sealing member  51 . A leading end portion of the rod portion  50  protrudes into the lock chamber  10 . The second valve element  49  includes a valve element body  52  having a flange portion  53 . A surface of the flange portion  34 , which is opposite from the rod portion  50 , is a valve surface  53   a . An annular sealing member  54  functioning as a valve seat member is fitted inside the second valve case  47 . The air discharge passage  18  is communicatively connected to the valve chamber  48 . A compression spring  55 , functioning as a biasing means and attached between a bottom surface of the second valve case  47  and the valve element body  52 , biases the second valve element  49  in a direction in which the valve surface  53   a  moves away from a valve seat  54   a  of the sealing member  54 . 
     Furthermore, the second detection valve  13  is structured as follows to function as a throttle detection valve, which is a detection valve with a throttle. A throttle attachment hole  52   a  is provided at a central portion of an end portion of the valve element body  52 , which is opposite from the rod portion  50 . A throttle member  56  is fixed in the attachment hole  52   a . A hole  56   a  functioning as a throttle passage is provided in the throttle member  56 . The hole  56   a  is communicatively connected to a throttle communication passage  52   b  provided in the valve element body  52 . The hole  56   a  opens to a portion of the valve chamber  48 , which is closer to the air passage  15 . The communication passage  52   b  opens to a portion of the valve chamber  48 , which is closer to the air discharge passage  18 . 
     The cylinder device having the above-described structure operates as follows.  
     In a release state shown in  FIG. 1 , pressurized oil has been discharged from the lock chamber  10  and pressurized oil has been supplied to the release chamber  11 . Due to this, the piston  5  has been moved downward by the pressurized oil in the release chamber  11 , and a lower end portion of the piston main body  6  is received from below by the lower end wall  3  of the housing  1 . 
     In the release state, the compression spring  36  of the first detection valve  12  has moved the engagement ball  32  toward the output rod  7  via the rod portion  30  of the first valve element  29 . Due to this, the valve surface  34   a  of the first valve element  29  is separated from the valve seat  35   a  of the sealing member  35 , and therefore the first detection valve  12  is open. 
     Meanwhile, the piston main body  6  of the piston  5  has moved the rod portion  50  of the second valve element  49  downward against the biasing force of the compression spring  55  of the second detection valve  13 . Due to this, the valve surface  53   a  of the second valve element  49  is tightly engaged onto the valve seat  54   a  of the sealing member  54 , and therefore the second detection valve  13  is closed. In this state, because the second detection valve  13  includes the throttle member  56  having the hole  56   a  functioning as the throttle passage, air leaks through the throttle passage, and therefore air flows through the air supply passage  17 , the air supply passage  16 , the first detection valve  12 , the air passage  14 , the air passage  15 , the second detection valve  13 , the air discharge passage  18 , and the air discharge passage  19 , in this order. Suppose that the pressure in the air supply passage  17  when the upstream first detection valve  12  is also closed is 0.2 MPa, for example. In the above situation in which: the first detection valve  12  is open; and the second detection valve  13  is closed, the pressure in the air supply passage  17  is lower than 0.2 MPa, and for example, it falls within a range from 0.15 MPa to 0.05 MPa. Such a pressure is detected by a pressure sensor (not shown), and based on this, the operational state of the piston  5  is determined as the release state. The threshold value for the pressure sensor for this determination is set to 0.15 MPa, for example. 
     To cause the device to transition from the release state shown in  FIG. 1  to the lock state shown in  FIG. 3 , pressurized oil is discharged from the release chamber  11  and pressurized oil is supplied to the lock chamber  10 . Then, the piston  5  starts to ascend due to the pressurized oil into the lock chamber  10 , and as shown in  FIG. 2 , the lower end portion of the piston main body  6  is separated from the lower end wall  3  of the housing  1 . Consequently, the compression spring  55  of the second detection valve  13  moves the second valve element  49  upward. Due to this, the valve surface  53   a  of the second valve element  49  is separated from the valve seat  54   a  of the sealing member  54 , to open the second detection valve  13 . As a result, the situation in which: the first detection valve  12  is open; and the second detection valve  13  is open, is established. This decreases the pressure in the air supply passage  17 , for example, to 0 MPa. Such a pressure is detected by the pressure sensor (not shown), and based on this, the operational state of the piston  5  is determined as a transitional state between the release state and the lock state. 
     As the piston  5  ascends, a leading end portion of the clamp arm  8  presses a to-be-clamped object W, as shown in  FIG. 3 . Then the ascent of the piston  5  stops and the device is into the lock state. In this state, a large-diameter portion  7   a  of the output rod  7  protruding from the piston main body  6  moves the first valve element  29  of the first detection valve  12  leftward via the engagement ball  32 . Due to this, the valve surface  34   a  of the first valve element  29  is tightly engaged onto the valve seat  35   a  of the sealing member  35 , so that the first detection valve  12  is closed. As a result, a situation in which: the first detection valve  12  is closed; and the second detection valve  13  is open is created. Air from the air supply passage  17  is stopped by the first detection valve  12 , and therefore the pressure in the air supply passage  17  in this situation is 0.2 MPa, for example. Such a pressure is detected by the pressure sensor (not shown), and based on this, the operational state of the piston  5  is determined as the lock state.  
     The output rod  7  includes a tapered surface portion  7   c  between the large-diameter portion  7   a  and a small-diameter portion  7   b , and this allows the first valve element  29  to move leftward smoothly. The pressure values of 0.15 MPa, 0 MPa, and 0.2 MPa mentioned above by way of example are automatically detectable using a single pressure sensor for which a plurality of threshold values can be set. 
     In the above embodiment, two threshold values (i.e., the first threshold value of 0.15 MPa and the second threshold value of 0.2 MPa) are set for the single pressure sensor to identify the operational state of the piston  5 . Instead, two pressure sensors, for each of which one threshold value is set, may be provided to a single passage, to identify the operational state of the piston  5 . 
       FIG. 6A  and  FIG. 6B  show a modification of the second detection valve  13  with the throttle. A second detection valve  57  (throttle detection valve) of this modification is different from the second detection valve  13  in the following points. 
     In this modification, a hole  58  functioning as the throttle passage is provided so as to pass through the second valve element  49  in the up-down direction. When the valve surface  53   a  of the second valve element  49  is tightly engaged onto the valve seat  54   a  of the sealing member  54 , the hole  58  acts as a small passage through which a small amount of air flows. The number of such holes  58  provided through the second valve element  49  may be one, or more than one. Alternatively, as shown in  FIG. 13A  and  FIG. 13B , a groove  70  functioning as the throttle passage may be provided on the valve surface  53   a  of the second valve element  49 . Here, similarly to the modification with the one or more holes  58 , the number of such grooves  70  provided on the valve surface  53   a  of the second valve element  49  may be one, or more than one. Furthermore, in the modification shown in  FIG. 13A  and  FIG. 13B , the one or more grooves  70  may be provided on the valve seat  54   a , instead of being provided on the valve surface  53   a . Similarly to the modification with the one or more grooves  70  provided on the valve surface  53   a , the number of the grooves  70  provided on the valve seat  54   a  may be one, or more than one. 
       FIG. 7  to  FIG. 12  show a second embodiment of the present invention. 
     A piston  59  structuring a cylinder device of the second embodiment has a rod hole  59   a  inside thereof, and a rod member  60  is inserted in the rod hole  59   a . The piston  59  includes: a piston main body  61 ; and an output rod  62  extending from the piston main body  61 . A compression spring  63  functioning as a biasing means biases the rod member  60  downward. The compression spring  63  is attached between a ceiling surface of the rod hole  59   a  and a flange portion  60   a  provided at an intermediate portion of the rod member  60 . An annular member  86  functioning as an operation portion for the rod member  60  is fitted in a lower end portion of the rod hole  59   a.    
     A first detection valve  64  and a second detection valve  65 , which are configured to detect the operational state of the piston  59 , are provided in the lower end wall  3  structuring the housing  1  (in a lower end portion of the housing  1 ). An air passage  66  that communicatively connects the first detection valve  64  and the second detection valve  65  to each other in series is provided in the lower end wall  3 . 
     Air supply passages  67  and  68 , through which air (compressed air) functioning as fluid for detection is supplied to the first detection valve  64  and to the second detection valve  65  in this order, are provided in a lower portion of the side wall of the housing main body  2  and in the lower end wall  3 , respectively. An air supply port  67   a  of the air supply passage  67  is communicatively connected to the air supply passage  17  provided in the stationary stand T. An air discharge passage  69 , through which air having been supplied to the detection valves  64  and  65  from the air supply passages  67  and  68  is discharged, is provided in the lower end wall  3 . An air discharge port  69   a  of the air discharge passage  69  is communicatively connected to the air discharge passage  19  provided in the stationary stand T. 
     The first detection valve  64  is structured as follows, as shown in  FIG. 10  to  FIG. 12 . 
     A first attachment hole  71  is provided in the lower end wall  3  so as to extend in the up-down direction. The first attachment hole  71  includes: a large-diameter hole  72  with an internal thread portion  72   a ; a middle-diameter hole  73 ; and a small-diameter hole  74 , which are provided in this order from the bottom side of the lower end wall  3 . A tubular pressing member  76  is screwed to a first valve case  77 . The tubular pressing member  76  is fixed to a step portion  75  between the internal thread portion  72   a  and the middle-diameter hole  73  by the first valve case  77  screwed to the internal thread portion  72   a . A valve chamber  78  is provided inside the first valve case  77  and inside the tubular pressing member  76 . The air supply passage  68  is communicatively connected to the valve chamber  78 . A first valve element  79  is inserted in the valve chamber  78 . A rod portion  80  of the first valve element  79  is movably inserted in the middle-diameter hole  73  via a sealing member  81 . As shown in  FIG. 11  and  FIG. 12 , a leading end portion of the rod portion  80  protrudes into the lock chamber  10 . An outer peripheral surface of an O-ring  83  fitted in an outer peripheral groove  82   a  of a valve element body  82  of the first valve element  79  is a valve surface  83   a . A protruding portion  84  functioning as a valve seat portion is provided on an inner peripheral wall of the tubular pressing member  76 . Furthermore, the air passage  66  is communicatively connected to the valve chamber  78 . A compression spring  85 , functioning as a biasing means and attached between a bottom surface of the first valve case  77  and the valve element body  82 , biases the first valve element  79  in a direction in which the valve surface  83   a  moves away from a valve seat  84   a  of the protruding portion  84 .  
     The second detection valve  65  is structured as follows, as shown in  FIG. 10  and  FIG. 12 . 
     A second attachment hole  91  is provided in the lower end wall  3  so as to extend in the up-down direction. The second attachment hole  91  includes: a large-diameter hole  92  with an internal thread portion  92   a ; a middle-diameter hole  93 ; and a small-diameter hole  94 , which are provided in this order from the bottom side of the lower end wall  3 . A tubular pressing member  96  is screwed to a second valve case  97 . The tubular pressing member  96  is fixed to a step portion  95  between the internal thread portion  92   a  and the middle-diameter hole  93  by the second valve case  97  screwed to the internal thread portion  92   a . A valve chamber  98  is provided inside the second valve case  97  and inside the tubular pressing member  96 . The air passage  66  is communicatively connected to the valve chamber  98 . A second valve element  99  is inserted in the valve chamber  98 . A rod portion  100  of the second valve element  99  is movably inserted in the middle-diameter hole  93  via a sealing member  101 . As shown in  FIG. 12 , a leading end portion of the rod portion  100  protrudes into the lock chamber  10 . An outer peripheral surface of an O-ring  103  fitted in an outer peripheral groove  102   a  of a valve element body  102  of the second valve element  99  is a valve surface  103   a . A protruding portion  104  functioning as a valve seat portion is provided on an inner peripheral wall of the tubular pressing member  96 . The air discharge passage  69  is communicatively connected to the valve chamber  98 . A compression spring  105 , functioning as a biasing means and attached between a bottom surface of the second valve case  97  and the valve element body  102 , biases the second valve element  99  in a direction in which the valve surface  103   a  moves toward a valve seat  104   a  of the protruding portion  104 . 
     Furthermore, the second detection valve  65  is structured as follows, to function as a throttle detection valve. A throttle passage  106  communicatively connecting the air passage  66  to the valve chamber  98  is provided in a portion of the tubular pressing member  96 , which is on a back side relative to the protruding portion  104 . 
     The cylinder device having the above-described structure operates as follows. 
     In the release state shown in  FIG. 7 , pressurized oil has been discharged from the lock chamber  10  and pressurized oil has been supplied to the release chamber  11 . Due to this, the piston  59  has been moved downward by the pressurized oil in the release chamber  11 , and a lower end portion of the piston main body  61  is received from below by the lower end wall  3  of the housing  1 . Furthermore, the rod member  60  inside the piston  59  is pressed onto the lower end wall  3  due to the biasing force of the compression spring  63 . 
     In the release state, the piston main body  61  of the piston  59  has moved the rod portion  80  of the first valve element  79  downward against the biasing force of the compression spring  85  of the first detection valve  64 . Due to this, the valve surface  83   a  of the O-ring  83  structuring the first valve element  79  is tightly engaged onto the valve seat  84   a  of the protruding portion  84  of the tubular pressing member  76 , so that the first detection valve  64  is closed. Meanwhile, the rod member  60  has moved the rod portion  100  of the second valve element  99  downward against the biasing force of the compression spring  105  of the second detection valve  65 . Due to this, the valve surface  103   a  of the O-ring  103  structuring the second valve element  99  is separated from the valve seat  104   a  of the protruding portion  104  of the tubular pressing member  96 , so that the second detection valve  65  is open. 
     Because the first detection valve  64  is closed, air supplied from the air supply passage  17  is stopped by the first detection valve  64 , and therefore the pressure in the air supply passage  17  in this situation is 0.2 MPa, for example. Such a pressure is detected by a pressure sensor (not shown), and based on this, the operational state of the piston  59  is determined as the release state.  
     To cause the device to transition from the release state shown in  FIG. 7  to the lock state shown in  FIG. 9 , pressurized oil is discharged from the release chamber  11  and pressurized oil is supplied to the lock chamber  10 . Then, the piston  59  starts to ascend due to the pressurized oil into the lock chamber  10 , and as shown in  FIG. 8 , the lower end portion of the piston main body  61  is separated from the lower end wall  3  of the housing  1 . Consequently, the compression spring  85  of the first detection valve  64  moves the first valve element  79  upward. Due to this, the valve surface  83   a  of the O-ring  83  structuring the first valve element  79  is separated from the valve seat  84   a , to open the first detection valve  64 . Meanwhile, the rod member  60  inside the piston  59  is still pressed onto the lower end wall  3  by the biasing force of the compression spring  63 , and therefore the second detection valve  65  is open. As a result, the situation in which: the first detection valve  64  is open; and the second detection valve  65  is open, is established. This decreases the pressure in the air supply passage  17 , for example, to 0 MPa. Such a pressure is detected by the pressure sensor (not shown), and based on this, the operational state of the piston  59  is determined as the transitional state between the release state and the lock state. 
     As the piston  59  ascends, the annular member  86  fitted in the lower end portion of the rod hole  59   a  of the piston main body  61  comes into contact, from below, with an under surface of the flange portion  60   a  provided at the intermediate portion of the rod member  60 , as shown in  FIG. 8 . As the piston  59  ascends further, the leading end portion of the clamp arm  8  presses a to-be-clamped object W, as shown in  FIG. 9 . Then the ascent of the piston  59  stops and the device is into the lock state. In this state, the piston main body  61  has moved the rod member  60  upward via the annular member  86  against the biasing force of the compression spring  63 . Due to this, the compression spring  105  of the second detection valve  65  moves the second valve element  99  upward, and this causes the valve surface  103   a  of the O-ring  103  structuring the second valve element  99  to be tightly engaged onto the valve seat  104   a , to close the second detection valve  65 . Because the second detection valve  65  has the throttle passage  106 , a small amount of air flows through the air supply passage  17 , the air supply passage  67 , the air supply passage  68 , the first detection valve  64 , the air passage  66 , the second detection valve  65 , the air discharge passage  69 , and the air discharge passage  19 , in this order. The pressure in the air supply passage  17  in this situation is lower than 0.2 MPa, for example, is 0.15 MPa. Such a pressure is detected by the pressure sensor (not shown), and based on this, the operational state of the piston  59  is determined as the lock state. 
     The pressure values of 0.2 MPa, 0 MPa, and 0.15 MPa mentioned above by way of example are automatically detectable using a single pressure sensor for which a plurality of threshold values can be set. 
       FIG. 15  to  FIG. 19B  show a third embodiment of the present invention. 
     This embodiment deals with a case in which the cylinder device of the present invention is applied to a rotary clamp, by way of example. A piston  150  inserted in the housing  1  structuring the cylinder device of the third embodiment has a rod hole  150   a  in its lower portion. A rod member  113  is inserted in the rod hole  150   a . The piston  150  includes: a piston main body  151 ; and an output rod  108  hermetically inserted in and fixed to a tubular hole  151   a  of the piston main body  151 . A compression spring  114  functioning as a biasing means biases the rod member  113  downward. The compression spring  114  is attached between a ceiling surface of the rod hole  150   a  and a flange portion  113   a  provided at an intermediate portion of the rod member  113 . The rod member  113  is configured to be lifted via an annular member  115  fitted in a lower end portion of the rod hole  150   a.    
     A clamp arm  109  is fixed to a leading-end-side portion of the output rod  108  with a nut  110 . A lower end portion of the output rod  108  is inserted in a support hole  3   a  provided in the lower end wall  3  of the housing  1 . Pressurized oil functioning as pressure fluid for locking is supplied to and discharged from a lock chamber  111 , provided above the piston main body  151 , through a lock passage  111   a . Furthermore, pressurized oil functioning as pressure fluid for releasing is supplied to and discharged from a release chamber  112 , provided between the piston main body  151  and the lower end wall  3 , through a release passage  112   a.    
     An output rod rotating mechanism  116  is provided at a portion of the output rod  108 , which is on a base end side relative to a flange portion  108   a . That is, the output rod rotating mechanism  116  is provided at the lower end portion of the output rod  108 . The output rod rotating mechanism  116  is structured as follows. 
     At least one guide groove  117  provided on an outer wall of the output rod  108  includes a straight linear groove  117   a  and a spiral rotation groove  117   b  that are provided continuously so that the linear groove  117   a  is above the rotation groove  117   b . At least one lateral hole  118  is provided at an upper portion of a peripheral wall of the support hole  3   a . An engagement ball  119  inserted in the lateral hole  118  is fitted in the guide groove  117 . A sleeve  120  is rotatably fitted over an outer periphery of the engagement ball  119 . 
     A first detection valve  121  and a second detection valve  122 , which are configured to detect the operational state of the piston  150 , are respectively provided above the side wall of the housing main body  2  and in the lower end wall  3 . Air (compressed air) functioning as fluid for detection and supplied from a compressed air supply source passes through air passages  123  to  128  and then is discharged to an outside of the housing  1  (to the outside). 
     The first detection valve  121  shown in  FIG. 18A  and  FIG. 18B  is similar to the first detection valve  64  shown in  FIG. 10  to  FIG. 12 . The first detection valve  121  is structured as follows.  
     A tubular pressing member  130  is fixed to a first attachment hole  129  by a first valve case  131 , which is screwed to an internal thread portion  129   a  of the first attachment hole  129  provided in the housing main body  2  so as to extend in a left-right direction. A valve element body  133   a  of a first valve element  133  is hermetically inserted in a valve chamber  132  provided inside the first valve case  131  and inside the tubular pressing member  130 . The air passage  124  and the air passage  125  are communicatively connected to the valve chamber  132 . A rod portion  133   b  is provided to protrude rightward from the valve element body  133   a , and a leading end portion of the rod portion  133   b  protrudes into the lock chamber  111 . The valve chamber  132  and the lock chamber  111  are separated from each other by a sealing member  152 . A compression spring  135  is attached between the first valve case  131  and a bottom surface of an attachment hole provided at a left portion of the first valve element  133 . The compression spring  135  biases the first valve element  133  in a direction in which a valve surface  136   a  of a sealing member  136  moves away from a valve seat  134   a  of a protruding portion  134  of the tubular pressing member  130 . 
     Furthermore, a communication passage  137  is provided in the first valve element  133 . The communication passage  137  communicatively connects the lock chamber  111  to a first hydraulic chamber  138  provided to the left of the first valve element  133 . This allows pressurized oil supplied to the lock chamber  111  to be supplied to the first hydraulic chamber  138  through the communication passage  137 . Here, a pressure receiving area of the valve element body  133   a  (the area of a section of the valve element body  133   a , which is orthogonal to its axis) is designed to be larger than a pressure receiving area of the rod portion  133   b  (the area of a section of the rod portion  133   b , which is orthogonal to its axis). Because of this, the first valve element  133  is moved so as to protrude into the lock chamber  111  by the force of the difference between: a force of the pressurized oil in the lock chamber  111  pushing the first valve element  133  leftward; and a force of the pressurized oil in the first hydraulic chamber  138  pushing the first valve element  133  rightward.  
     The second detection valve  122  shown in  FIG. 19A  and  FIG. 19B  is similar to the second detection valve  65  shown in  FIG. 10  to  FIG. 12 . The second detection valve  122  is structured as follows. 
     A tubular pressing member  140  is fixed to a second attachment hole  139  by a second valve case  141 , which is screwed to an internal thread portion  139   a  of the second attachment hole  139  provided in the lower end wall  3  of the housing  1  so as to extend in the up-down direction. The air passage  126  and the air discharge passage  127  are communicatively connected to a valve chamber  142  in the second detection valve  122 . A valve element body  143   a  of a second valve element  143  is hermetically inserted in the valve chamber  142 . A leading end portion of a rod portion  143   b , provided to protrude upward from the valve element body  143   a , protrudes into the release chamber  112 . A compression spring  145  is attached between a bottom surface of the second valve case  141  and an attachment hole provided in the valve element body  143   a . The compression spring  145  biases the second valve element  143  in a direction in which a valve surface  146   a  of a sealing member  146  is separated from a valve seat  144   a  of a protruding portion  144  of the tubular pressing member  140 . 
     Furthermore, a communication passage  147  provided in the second valve element  143  communicatively connects the release chamber  112  to a second hydraulic chamber  148  provided below the second valve element  143 . This allows pressurized oil supplied to the release chamber  112  to be supplied to the second hydraulic chamber  148  through the communication passage  147 . Here, a pressure receiving area of the valve element body  143   a  (the area of a section of the valve element body  143   a , which is orthogonal to its axis) is designed to be larger than a pressure receiving area of the rod portion  143   b  (the area of a section of the rod portion  143   b , which is orthogonal to its axis). Because of this, the second valve element  143  is moved so as to protrude into the release chamber  112  by the force of the difference between: a force of the pressurized oil in the release chamber  112  pushing the second valve element  143  downward; and a force of the pressurized oil in the second hydraulic chamber  148  pushing the second valve element  143  upward. 
     Furthermore, the second detection valve  122  is structured as follows to function as a throttle detection valve. A throttle passage  149  communicatively connecting the air passage  126  to the air passage  127  is provided in a portion of the tubular pressing member  140 , which is on a back side relative to the protruding portion  144 . 
     The cylinder device having the above-described structure operates as follows. 
     To cause the device to transition from the release state shown in  FIG. 15  to the lock state shown in  FIG. 17 , pressurized oil is discharged from the release chamber  112  and pressurized oil is supplied to the lock chamber  111 . Then, the pressurized oil supplied to the lock chamber  111  causes the piston main body  151  to move the output rod  108  downward. At the beginning, the output rod  108  descends while rotating in a clockwise direction due to the presence of the output rod rotating mechanism  116 . After the piston main body  151  descends a small distance while rotating, the first valve element  133  is moved rightward by a force of the difference between the leftward pushing force by the pressurized oil in the lock chamber  111  and the rightward pushing force by the pressurized oil in the first hydraulic chamber  138  of the first detection valve  121 , and by the rightward biasing force by the compression spring  135 . As a result, the first detection valve  121  is opened, as shown in  FIG. 18B . At this moment, the second detection valve  122  is also open, as shown in  FIG. 19A . Due to this, compressed air from the compressed air supply source is discharged to the outside through the air passages  123  to  128 . A switch configured to detect the pressure in the air passage  123  or the like detects that the pressure in the air passage is below a first set pressure (first threshold value). As the output rod  108  descends further while rotating, a leading end portion of the clamp arm  109  is moved to a position above a to-be-clamped object W, as shown in FIG.  16 . At this moment, a lower end surface of the rod member  113  is in contact with an upper end surface of the second valve element  143  of the second detection valve  122 , or there is a small gap between these surfaces. Subsequently, as the piston main body  151  descends straight, the clamp arm  109  presses the object W from above. Then the descent of the output rod  108  stops and the device is into the lock state. In this state, the piston main body  151  pushes and moves the second valve element  143  of the second detection valve  122  downward via the rod member  113 , and meanwhile the rod member  113  is inserted into the rod hole  150   a  of the output rod  108  against the biasing force of the compression spring  114 . As a result, the second valve surface  146   a  of the second detection valve  122  is brought into contact with the second valve seat  144   a , to close the second detection valve  122 . Due to this, compressed air from the compressed air supply source passes through the air passages  123  to  127  and through the throttle passage  149 , and then is discharged to the outside through the air passage  128 . In this state, the switch detects that: the pressure in the air passage is higher than the first set pressure (first threshold value); but is below a second set pressure (second threshold value), which has been set to be higher than the first set pressure. 
     To cause the device to transition from the lock state shown in  FIG. 17  to the release state shown in  FIG. 15 , pressurized oil is discharged from the lock chamber  111  and pressurized oil is supplied to the release chamber  112 . Then, the piston main body  151  ascends straight upward due to the pressurized oil into the release chamber  112 . However, the output rod  108  pushes the rod member  113  downward via the compression spring  114 , and therefore the rod member  113  is left at a lower end position. After the piston main body  151  ascends further to a position at which the annular member  115  is brought in contact with the flange portion  113   a  of the rod member  113 , the output rod  108  lifts the rod member  113  via the annular member  115 . At this moment, the second valve element  143  is raised by a force of the difference between: the downward pushing force by the pressurized oil in the release chamber  112 ; and the upward pushing force by the pressure in the second hydraulic chamber  148 , so that the second detection valve  122  is opened. Subsequently, the piston  150  ascends while rotating in a counterclockwise direction due to the presence of the output rod rotating mechanism  116 . When the piston main body  151  moves to a position slightly below its upper limit position, the piston main body  151  comes into contact with the rod portion  133   b  of the first detection valve  121 . Then, the piston main body  151  moves the first valve element  133  leftward, to close the first detection valve  121 . The piston main body  151  is received by an upper wall of the housing  1 , which stops the ascent of the output rod  108 , and the device is into the release state. In this state, the switch detects that the pressure in the air passage  123  exceeds the second set pressure. 
     The first detection valve  121  includes the compression spring  135 . Due to this, the rightward biasing force of the compression spring  135  keeps the first valve element  133  protruding into the lock chamber  111  when the pressurized oil in the first hydraulic chamber  138  is discharged through the lock chamber  111 . The second detection valve  122  also includes the compression spring  145 . Due to this, in the same manner as in the first detection valve  121 , the upward biasing force of the compression spring  145  keeps the second valve element  143  protruding into the release chamber  112 . 
     The above-described embodiments are changeable as follows. 
     In the cylinder device of the first embodiment, the first detection valve  12  and the second detection valve  13  (throttle detection valve) may be replaced with each other. Specifically, the second detection valve  13  (throttle detection valve) may be disposed upstream, and the first detection valve  12  may be disposed downstream. The same applies to the third embodiment.  
     In the cylinder device of the first embodiment, the route of the air passages  14  and  15  that connect the detection valves  12  and  13  to each other in series may be changed in the housing  1 . The same applies to the third embodiment. 
     Instead of the configuration in which air is supplied to the detection valves  12  and  13 ,  64  and  65 ,  121  and  122  from the air supply passage  16 ,  67 ,  124  and then is discharged to the air discharge passage  18 ,  69 ,  127 , the following configuration is also possible in each of the embodiments: air is supplied from the side of the air discharge passage  18 ,  69 ,  127  to the detection valves  12  and  13 ,  64  and  65 ,  121  and  122 , and then is discharged to the side of the air supply passage  16 ,  67 ,  124 . More specifically, taking the first embodiment as an example, each embodiment is changeable as follows. Instead of the configuration in which air passes through the air supply passage  16  and through the detection valves  12  and  13  in this order, and then air is discharged through the air discharge passage  18 , arrangement may be made so that air passes through the air supply passage  16  and through the detection valves  13  and  12  in this order, and then air is discharged through the air discharge passage  18 . 
     As for the second detection valve  13  (throttle detection valve) of the cylinder device of the first embodiment, the second valve element  49  and the throttle member  56  may be unitary with each other. That is, these elements may be made of one material. 
     The second detection valve  13  (throttle detection valve) has the throttle passage (hole  56   a ) provided in the detection valve  13 . Instead of the configuration in which the throttle passage is provided in the detection valve  13 , the throttle detection valve with the throttle passage may have a configuration shown in  FIG. 14 : a throttle member  107  for the detection valve is provided outside the detection valve  13 , for example, to the housing  1 ; and a throttle passage  107   a  is provided in the throttle member  107 . 
     The cylinder device of the first embodiment may be arranged so that: no engagement ball  32  is provided; and the large-diameter portion  7   a  of the output rod  7  directly pushes the rod portion  30  of the first valve element  29  of the first detection valve  12 . 
     In the cylinder device of the first embodiment, the first detection valve  64  of the cylinder device of the second embodiment may be used instead of the first detection valve  12 . In the cylinder device of the second embodiment, the first detection valve  12  of the cylinder device of the first embodiment may be used instead of the first detection valve  64 . 
     The second detection valve  65  of the cylinder device of the second embodiment is a normally closed (NC) throttle detection valve, which is closed when no external force is applied. A normally open (NO) valve, which is open when no external force is applied, may be used for the second detection valve  65 , and such a normally open (NO) throttle detection valve may be used instead of the second detection valve  13  in the cylinder device of the first embodiment. 
     In each of the above-described embodiments, two detection valves are used to detect the operational state of the piston (the lock state/release state). Another detection valve may be added for the detection of an overstroke of the piston, in addition to the detection of the lock state/release state. That is, the cylinder device may be arranged to include three or more detection valves. 
     The first detection valve  12 ,  64  and the second detection valve  13 ,  65  (spring operated detection valves) of each of the cylinder devices of the first and second embodiments may be replaced by the first detection valve  121  and the second detection valve  122  (hydraulically operated detection valves) of the cylinder device of the third embodiment, respectively. 
     Pressure fluid for locking/releasing may be compressed gas such as compressed air and compressed nitrogen gas, instead of pressurized oil. 
     The cylinder device of the present invention may be applied to clamps other than the link clamp and the rotary clamp. Furthermore, the application is not limited to clamps. The present invention may be applied to other actuators such as a reciprocating device driven by an electric motor and ball screw shafts, gears, and the like. 
     Embodiments and modifications of the present invention have been hereinabove described. It is a matter of course that other changes or alterations can be made on the present invention within the scope of envisagement of one skilled in the art. 
     REFERENCE SIGNS LIST 
       1 : housing;  5 : piston;  12 : first detection valve (detection valve);  13 : second detection valve (throttle detection valve);  14 : air passage;  15 : air passage;  48 : valve chamber;  49 : second valve element (valve element);  50 : rod portion;  52 : valve element body;  53   a : valve surface;  54   a : valve seat;  55 : compression spring (biasing means);  56 : throttle member;  56   a : hole (throttle passage);  57 : second detection valve (throttle detection valve);  58 : hole (throttle passage);  59 : piston;  64 : first detection valve (detection valve);  65 : second detection valve (throttle detection valve);  66 : air passage;  70 : groove (throttle passage);  106 : throttle passage;  107 : throttle member;  107   a : throttle passage;  121 : first detection valve (detection valve);  122 : second detection valve (throttle detection valve);  125 : air passage;  126 : air passage;  149 : throttle passage;  150 : piston.