Patent Publication Number: US-7216580-B2

Title: Multistage stroke cylinder apparatus

Description:
TECHNICAL FIELD 
   The present invention relates to a multistage stroke cylinder apparatus suitable for use in which a stroke of a cylinder needs to be adjusted in a plurality of stages like in a gun cylinder or the like in a spot welding device. 
   PRIOR ART 
   A movable-side electrode in a spot welding device needs to have at least two stages of stop positions with respect to a fixed-side electrode. In other words, in a gun cylinder, it is necessary to occupy a fully open position where the electrodes of a pair are open when an object to be welded is sandwiched between the electrodes, a welding preparatory position where the electrodes of the pair are caused to face the object to be welded positioned between the electrodes through relatively short working strokes so as to minimize a length of the stroke to carry out a plurality of times of spot welding, and a welding operating position where both the electrodes are pressed against the object. 
   In welding operation under present circumstances, it is also required to increase a degree of freedom of a welding stroke to be adaptable to many kinds of members to be welded and a demand for an electric (servo) welding gun for achieving it is growing. However, the electric (servo) welding gun under present circumstances has a price problem, problems of deposition accidents in line operations, and problems in terms of practicality such as difficulty in handling. 
   The above-described problems are found not only in the spot welding gun cylinder but also in a device such as a pressurizing unit of various clamping devices in which a head mounted to a tip end of a main rod is repeatedly pushed against a workpiece. In this case, there are similar problems. 
   DISCLOSURE OF THE INVENTION 
   An object to be achieved by the present invention is basically to provide a simple mechanism for solving the above problems to a prior-art fluid pressure cylinder for a spot welding gun or the like. 
   It is a further concrete object of the invention to provide a multistage stroke cylinder apparatus which has at least two stages of stop positions with respect to an object and in which a freedom of a stroke is increased so as to be adaptable to many kinds of members to be welded. 
   It is another object of the invention to provide a multistage stroke cylinder apparatus less expensive and with better operability than an electric (servo) welding gun. 
   It is another object of the invention to provide a multistage stroke cylinder apparatus having a cushioning mechanism to be adaptable to reduction of wear of a welding rod and other tools and diminishing of a collision sound. 
   It is another object of the invention to provide a multistage stroke cylinder in which each stroke can be adjusted by remote operation which is supply and discharge of fluid by a solenoid valve. 
   It is another object of the invention to provide a multistage stroke cylinder apparatus in which an operating form of the main rod operating in a complicated manner can be detected. 
   To achieve the above objects, according to the invention, there is provided a multistage stroke cylinder apparatus comprising: a main cylinder including a main piston housed for sliding in a cylinder tube and driven by fluid pressure supplied to pressure chambers on opposite sides of the main piston and a main rod connected to the main piston, a head cover and a rod cover being mounted to opposite ends of the cylinder tube; an intermediate stop position setting mechanism for setting an intermediate stop position of the main piston; and a return position setting mechanism for setting a return position of the main piston, wherein the intermediate stop position setting mechanism includes a stop position setting piston disposed for sliding between the main piston in the cylinder tube and the head cover to define the intermediate stop position of the main piston by coming in contact with the main piston, an auxiliary rod connected to the stop position setting piston and having a tip end passing through the head cover and extending outside, a stopper fitted with the tip end of the auxiliary rod to stop the stop position setting piston in a necessary position by coming in contact with a contact portion of the head cover, and a changing mechanism for changing a stop position of the stop position setting piston by the stopper and the return position setting mechanism includes a return position setting piston provided for sliding to the head cover and a position setting rod connected to the return position setting piston and having a tip end projecting behind the stop position setting piston. 
   In a concrete example of the invention, the changing mechanism has at least one of a mechanism for changing a mounting position of the stopper on the auxiliary rod and a mechanism for changing a position of the contact portion by a contact position adjusting piston. 
   To put it more concretely, the mechanism for changing the mounting position of the stopper has a plurality of stepped portions formed on opposite sides of an inner hole of the stopper and having different depths and a stepped portion formed on an outer periphery of the auxiliary rod and is formed to be able to change the mounting position of the stopper on the auxiliary rod by changing an orientation of the stopper to selectively bring any of the stepped portions into-contact with the stepped portion of the auxiliary rod. The mechanism for changing the position of the contact portion has the contact position adjusting piston having the contact portion and the adjusting piston is mounted to the head cover and driven by fluid pressure in such directions as to approach and move away from the stopper. 
   According to another concrete embodiment of the invention, the auxiliary rod passes for sliding through the return position setting piston and the position setting rod and projects outside the head cover and has a flow path connecting a port for supplying pressure fluid and the pressure chamber on one side of the main piston in the auxiliary rod. 
   In the multistage stroke cylinder apparatus of the invention, the main cylinder may have a cushioning mechanism for reducing a speed of the main piston by restricting a discharge flow rate of fluid discharged from a discharge-side pressure chamber at an end of a stroke of the main piston. 
   It is also possible that the main cylinder has a stroke detector for outputting an electric signal according to a stroke position of the main rod and that the stroke detector is connected to a detection controller for detecting an operating form of the main rod based on the output. 
   Furthermore, it is possible to attach a balance mechanism to the cylinder apparatus, the balance mechanism being for causing the stop position setting piston to stop in a position where the stop position setting piston has moved toward the main piston when pressure fluid at the same pressure is supplied to pressure chambers on opposite sides of the stop position setting piston in order to eliminate necessity of consideration of a degree of fluid pressure supplied to each the pressure chamber in connection with a difference between the pressure receiving areas on opposite sides of the stop position setting piston. 
   In the multistage stroke cylinder apparatus having the above structure, the main rod is driven in an axial direction by driving by fluid pressure of the main piston. In order to set the intermediate stop position of the main piston, the stop position setting piston with which the main piston comes in contact and stops is provided, the auxiliary rod extending from the piston extends outside from the head cover, and the stopper is mounted to the tip end of the auxiliary rod. Therefore, by bringing the stopper into contact with the contact portion of the head cover to position the stop position setting piston, the stop position of the main piston can be set. Furthermore, because the stop position of the stop position setting piston defined by the stopper can be changed, the intermediate stop position of the main rod can be adjusted. 
   As the return position setting mechanism for setting the return position of the main piston, the tip end of the position setting rod connected to the return position setting piston is caused to face a back of the stop position setting piston to set the return position of the main piston. Therefore, by driving or non-driving of the return position setting piston, the return position of the main piston can be adjusted in two positions, i.e., the full stroke of the main cylinder can be adjusted in two stages. 
   As a result, according to the invention, it is possible to obtain the multistage stroke cylinder apparatus which has at least two stages of stop positions with respect to the object and in which the degree of freedom of the stroke is increased so as to be adjustable to many kinds of members to be welded. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a partial sectional view of an entire structure of a first embodiment of a cylinder apparatus according to the present invention. 
       FIG. 2  is an enlarged vertical sectional view of an essential portion (main cylinder) taken in a different direction from  FIG. 1  of the first embodiment. 
       FIG. 3  is a vertical sectional view of an essential portion (intermediate stop position setting means) in the first embodiment. 
       FIG. 4  is an enlarged vertical sectional view of an essential portion (cushioning mechanism) in a different position from  FIG. 2  of the first embodiment. 
       FIG. 5  is an explanatory view for explaining an example of a form of operation of a multistage stroke cylinder according to the invention. 
       FIG. 6  is a sectional view of an essential portion of a second embodiment in which balance means for eliminating necessity of pressure adjustment of fluid to each supply/discharge port is added to the multistage stroke cylinder of the first embodiment. 
       FIG. 7  is a partial half sectional view of a structure of a third embodiment of the multistage stroke cylinder according to the invention. 
       FIG. 8  is a partial half sectional view of a structure of a fourth embodiment of the multistage stroke cylinder according to the invention. 
   

   DETAILED DESCRIPTION 
     FIGS. 1 to 4  show a first embodiment of multistage stroke cylinder apparatus according to the present invention. The cylinder apparatus is a cylinder apparatus driven by pressure of fluid such as air and suitable for use in a case in which a plurality of stages of strokes and adjustable strokes are required like in a gun cylinder for spot welding. The cylinder apparatus includes a main cylinder  1  (see  FIGS. 1 and 2 ) having a main piston  12  for sliding in a sealed state in a cylinder tube  10  and a main rod  13  passing through a rod cover  11  of the cylinder tube  10  and driven in an axial direction. To the main cylinder  1 , an intermediate stop position setting mechanism  2  for setting an intermediate stop position of the main piston  12  and a return position setting mechanism  4  for setting a return position of the main piston  12  are attached. 
   The intermediate stop position setting mechanism  2  has a stop position setting piston  21  housed for sliding in a sealed state in a position facing the main piston  12  in the cylinder tube  10  and an auxiliary rod  22  connected to the piston  21 . The auxiliary rod  22  extends through a head cover  14  of the cylinder tube  10  to an outside and a stopper  23  is mounted to a tip end of the auxiliary rod  22 . The stopper  23  comes in contact with a contact portion  31   a  of a contact position adjusting piston  31 . By this contact, a stop position of the stop position setting piston  21 , i.e., the intermediate stop position of the main pist on  12  is set. 
   As clearly shown in  FIG. 3 , the stopper  23  is fixed by a nut  26  screwed over the auxiliary rod  22  in a state in which the auxiliary rod  22  is inserted into a hole  23   a  at a center of the stopper  23  and stepped portions  24  formed at end portions of the hole  23   a  are brought into contact with a stepped portion  25  formed on a peripheral face of the auxiliary rod  22 . In the drawing, a reference numeral  29  designates a damper. 
   The stepped portions  24  are formed respectively on opposite sides of the hole  23   a  and are at different distances from hole ends, i.e., have different depths. By detaching the nut  26  and reversing the stopper  23  in a longitudinal direction, a mounting position of the stopper  23  on the auxiliary rod  22  can be changed and, as a result, a contact stroke of the stopper  23  with respect to the contact position adjusting piston  31 , i.e., a stroke of the stop position setting piston  21  can be changed.  FIGS. 1 and 3  show states in which orientations of the stopper  23  are reverse to each other and the piston  21  has different strokes from each other. Therefore, the stepped portions  24 ,  24  formed on opposite sides of the hole  23   a  of the stopper  23  and having different depths form a changing mechanism for changing the stop position of the stop position setting piston  21  together with the stepped portion  25  of the auxiliary rod  22 . 
   It is also possible to prepare a plurality of stoppers  23  having the stepped portions  24  with different depths and to variously change the stroke of the stop position setting piston  21  by exchanging the stoppers  23 . 
   The contact position adjusting piston  31  is housed for sliding with a small stroke in a cylinder-shaped cover  32  provided on an outer end side of the head cover  14  and the contact portion  31   a  on an outer end face of the contact position adjusting piston  31  is exposed outside from the cylinder-shaped cover  32  and faces the stopper  23 . The auxiliary rod  22  passes through a central hole of the piston  31  and the piston  31  can slide in a sealed state along and with respect to the auxiliary rod  22 . 
   The contact position adjusting piston  31  is driven by pressure fluid (compressed air) supplied from a port  35  provided to a supply/discharge block  34  of the head cover  14  to a pressure chamber  36  to displace the contact portion  31   a  between two positions, i.e., a projecting position and a return position to thereby change a stop position of the stopper  23 . Therefore, the contact position adjusting piston  31  also forms a changing mechanism for changing the stop position of the stop position setting piston  21 . As a result, by combining a position change of the contact portion  31   a  by the contact position adjusting piston  31  and a position change of the stopper  23  on the auxiliary rod  22  by selection of the stepped portions  24 ,  24 , it is possible to adjust the stop position of the stop position setting piston  21  in multiple stages. Especially, because position adjustment by the contact position adjusting piston  31  is carried out by supplying the pressure fluid from the port  35 , it is possible to carry out the position adjustment by remote operation of a valve. 
   Although adjustment of the stop position of the stop position setting piston  21  may be carried out by both means of changing a fixed position of the stopper  23  on the auxiliary rod  22  and means of changing the position of the contact portion  31   a  by the contact position adjusting piston  31 , it is also possible to carry out the adjustment by only one of the means. If the position of the contact portion  31   a  is not changed, the contact portion  31   a  can be directly mounted to the outer end face of the head cover  14 . 
   The stop position setting piston  21  is driven by supplying and discharging pressure fluid (compressed air) from and to a port  28  provided to a main body  41  in the head cover  14  to and from a pressure chamber  27  behind the piston  21 . In other words, the stop position setting piston  21  is moved to a predetermined intermediate stop position determined by the stopper  23  by supplying the pressure fluid from the port  28  to the pressure chamber  27  and the piston  21  is returned when the piston  21  is pressed by the returning main piston  12  in a state in which the pressure fluid is discharged through the port  28 . 
   The return position setting mechanism  4  for setting the return position of the main piston  12  is formed by disposing a return position setting piston  43  for sliding in a sealed state in a cylinder portion  41   a  provided in the main body  41  and causing a position setting rod  44  connected to the piston  43  to face a back of the stop position setting piston  21  through a damper  45 . The position setting rod  44  is fitted in a sealed state over an outer periphery of the auxiliary rod  22  of the stop position setting piston  21  and slides on the auxiliary rod  22 . Between the return position setting piston  43  and the supply/discharge block  34  in the head cover  14 , a driving-side pressure chamber  47  is formed. By supplying the pressure fluid such as compressed air to the pressure chamber  47  through a port  46  (in a different position from the port  35 ) for setting the return position, the piston  43  is driven and the position setting rod  44  occupies two positions, i.e., a projecting position for shortening an entire stroke of the main piston  12  and a return position for maximizing the stroke. 
   The cylinder apparatus includes a cushioning mechanism for reducing a speed of the main piston  12  at an end of the projecting stroke by restricting a discharge flow rate from a discharge-side pressure chamber  54 . 
   In other words, a cushion ring  51  is provided to the main piston  12 , a recessed portion  52  in which the cushion ring  51  is fitted is provided to the rod cover  11 , and cushion packing  53  for coming into contact with a peripheral face of the cushion ring  51  to cancel direct connection of the recessed portion  52  and the pressure chamber  54  on a side of the rod cover  11  in the cylinder tube  10  to each other when the cushion ring  51  enters the recessed portion  52  is provided to a mouth edge of the recessed portion  52 . As shown in  FIG. 2 , the recessed portion  52  has a port  55  for supplying compressed air to the pressure chamber  54  for returning the main piston  12  and the cushion packing  53  provides one-way sealing in which the compressed air from the port  55  is all owed to flow into the pressure chamber  54  while a flow of the compressed air from the pressure chamber  54  into the recessed portion  52  is intercepted. 
   As shown in  FIG. 4 , a throttle valve  57  for discharging the compressed air in the pressure chamber  54  through the recessed portion  52  to the port  55  in a cushioning stroke of the main piston  12  is provided in a flow path  56  for connecting the pressure chamber  54  and an inner side of the cushion packing  53  in the recessed portion  52 . Not only the throttle valve  57  but also a single or a plurality of groove(s) (not shown) on a peripheral face of the cushion ring  51  can be provided between the pressure chamber  54  and the recessed portion  52  to discharge through the groove(s). 
   On the other hand, a port  59  for supplying compressed air to a pressure chamber  58  on a side opposite to the main piston  12  is provided to an outer end of the auxiliary rod  22  connected to the stop position setting piston  21  and communicates with the pressure chamber  58  through a flow path  60  extending through the auxiliary rod  22 . 
   In this cushioning mechanism, the main piston  12  is driven by supplying the compressed air to the pressure chamber  58 . When the cushion ring  51  rushes into the cushion packing  53 , a flow path for directly discharging from the exhaust-side pressure chamber  54  through the port  55  is closed. Air remaining in the pressure chamber  54  is discharged only through the flow path  56  provided with the throttle valve  57  or the groove provided to the peripheral face of the cushion ring  51 . As a result, pressure in the pressure chamber  54  increases and the pressure exerts a cushioning operation on the main piston  12 . 
   Such a cushioning mechanism is effective on demands such as reduction of wear of a tool such as a welding rod and diminishing of a collision sound which a prior-art cylinder for a pneumatic spot welding gun or the like cannot satisfy. 
   If there is no necessity of provision of the cushioning mechanism, the main piston  12  does not need to be driven by the compressed air and it is possible to use arbitrary pressure fluid. 
   As shown in  FIG. 1 , the rod cover  11  is provided with a stroke detector  63 . The stroke detector  63  reads a magnetic scale attached onto the main rod  13  with a head  63   a  to thereby output an electric signal according to a stroke position of the main rod  13  and is connected to a detection controller. Based on the output, the detection controller can detect at which stroke the main rod  13  is operating, based on which not only an operating form of the multistage stroke cylinder but also a wear amount or the like of electrodes can be grasped based on a position of the main rod in pressurization of an object. There is no harm in using a detector for detecting the stroke by other measuring means. 
   In the cylinder apparatus having the above structure, the main rod  13  is driven basically by supplying pressure fluid such as compressed air to one of the pressure chambers  54  and  58  on opposite sides of the main piston  12  and discharging the compressed air from the other of the pressure chambers at the same time. To put it more concretely, by supplying the compressed air to the pressure chamber  58  of the main cylinder  1  from the port  59  at a tip end of the auxiliary rod  22  through the flow path  60  in the auxiliary rod  22 , the main rod  13  is driven in a projecting direction through the main piston  12 . By simultaneously discharging the compressed air of the pressure chamber  58  and supplying the compressed air to the other pressure chamber  54 , the main piston  12  and the main rod  13  are returned. 
   The intermediate stop position of the main piston  12  is set by the intermediate stop position setting mechanism  2 . In other words, if the compressed air is supplied from the port  28  provided to the head cover  14  to the pressure chamber  27  behind the stop position setting piston  21 , the stop position setting piston  21  moves to and stops in a position where the stopper  23  at the tip end of the auxiliary rod  22  connected to the piston  21  comes into contact with the contact portion  31   a  on the outer face of the contact position adjusting piston  31 . As a result, the stop position setting piston  21  moves to an intermediate position (a position shown in a chain line in  FIGS. 1 and 2 ) for setting the stop position of the main piston  12 . 
   The intermediate position where the stop position setting piston  21  stops can be adjusted in multiple stages by one or both of the above-described two changing mechanisms, i.e., a mechanism for changing the mounting position of the stopper  23  by selecting the stepped portion  24  of the stopper  23  and a mechanism for changing the contact position of the stopper  23  by the contact position adjusting piston  31 . To put it concretely, in the former changing mechanism, the adjustment can be done by detaching the nut  26  and reversing the stopper  23  in the longitudinal direction or by exchanging the stopper  23  for another stopper  23  having stepped portions  24  with different depths. In the latter changing mechanism, the contact position of the stopper  23  can be changed by supplying and discharging the pressure fluid to and from the pressure chamber  36  through the port  35  provided to the supply/discharge block  34  to drive the contact position adjusting piston  31  to thereby displace the contact portion  31   a  to the projecting position or the return position. By combining both the mechanisms, the stop position of the stop position setting piston  21  can be adjusted in multiple stages. 
   As described above, by changing the intermediate position where the stop position setting piston  21  stops by the changing mechanisms, it is possible to adjust a moving position of the stop position setting piston  21  when the pressure fluid is supplied from the port  28  to the pressure chamber  27  to thereby adjust the return position of the main piston  12 . 
   The return position of the main piston  12 , i.e., a full stroke of the main piston  12  is set by the return position setting mechanism  4 . To put it concretely, by supplying and discharging the pressure fluid to and from the pressure chamber  47  through the port  46  for setting the return position and provided to the supply/discharge block  34 , the return position setting piston  43  and the position setting rod  44  are moved forward or rearward and the tip end of the rod  44  is displaced to two positions, i.e., the projecting position and the return position behind the stop position setting piston  21  to thereby adjust the full stroke of the main cylinder in two stages. 
   In the cylinder apparatus, because a pressure receiving area of the contact position adjusting piston  31  on a side of the pressure chamber  36  is set to be larger than a pressure receiving area of the stop position setting piston  21  on a side of the pressure chamber  27 , the contact position adjusting piston  31  is not pushed back by a force received from the stopper  23  in a state in which the pressure fluid has been supplied from the port  35  to the pressure chamber  36  to drive the contact position adjusting piston  31 , the pressure fluid at the same pressure has been supplied from the port  28  to the pressure chamber  27  to drive the stop position setting piston  21 , and the stopper  23  has come in contact with the contact portion  31   a  of the contact position adjusting piston  31 . 
   However, in the state in which the pressure fluid has been supplied from the port  28  to the pressure chamber  27  to drive the stop position setting piston  21  and the stopper  23  has come in contact with the contact portion  31   a  of the contact position adjusting piston  31 , if the pressure fluid at the same pressure is supplied from the port  59  at the end portion of the auxiliary rod  22  through the flow path  60  in the auxiliary rod  22  to the pressure chamber  58 , the stop position setting piston  21  is pushed back by a force from the side of the pressure chamber  58  because the pressure receiving area of the stop position setting piston  21  on the side of the pressure chamber  58  is larger than the pressure receiving area on the side of the pressure chamber  27 . 
   Therefore, the pressure of the fluid supplied from the port  28  is preferably higher to such a degree as not to cause the above-described pushing back than the pressure of the fluid supplied from the port  59  and the pressure of fluid supplied from the port  35  is also preferable to be increased with this increase. 
     FIG. 5  shows an example of an operating form of the cylinder apparatus. In this example, by supplying the pressure fluid through the port  28  to the pressure chamber  27  from a stroke start position A of the full stroke set by the return position setting piston  43 , the stop position setting piston  21  is driven and thus, the main piston  12  is pushed by the stop position setting piston  21  and driven and reaches an intermediate stop position B. Then, by alternately repeating supply and discharge of the pressure fluid to and from the pressure chambers  58  and  54  on opposite sides of the main piston  12 , a working stroke of reciprocation between points B and C for multipoint welding or the like is repeated. When this repetition finishes, the pressure fluid in the pressure chamber  27  is discharged from the port  28  in a state in which the pressure fluid has been supplied to the pressure chamber  54  and the main piston  12  is returned to the original stroke start position. 
   In the above multistage stroke cylinder apparatus of the first embodiment, as described above, degrees of pressures of fluid supplied to the respective ports need to be adjusted in order to carry out necessary operation in connection with a difference between the pressure receiving areas on opposite sides of the stop position setting piston  21 . However, in second to fourth embodiments shown in  FIGS. 6 to 8 , a balance mechanism for eliminating necessity of such pressure adjustment by adjustment or the like of pressure receiving areas of the respective pistons, i.e., a mechanism for setting the stop position of the stop position setting piston when the pressure fluid at the same pressure is supplied to the pressure chambers on the opposite sides of the piston at a position where the piston has moved toward the main piston is attached to the intermediate stop position setting mechanism  2 . 
   First, the second embodiment in  FIG. 6  is one in which the above balance mechanism is added to the head cover  14  of the first embodiment. To put it concretely, the head cover  14  is provided with a cylinder-shaped cover  65  having a port  67  instead of the cylinder-shaped cover  32  of the first embodiment and a rod encapsulating tube  66  with which the auxiliary rod  22  is covered in a sealed state is attached to the cylinder-shaped cover  65 . The port  67  is connected to the rod encapsulating tube  66  and compressed air is supplied and discharged to and from the pressure chamber  58  from the port  67  through an inside of the encapsulating tube  66  and the port  59  at the tip end of the auxiliary rod  22 . Because the rod encapsulating tube  66  is provided, inner and outer peripheries of a shaft-shaped portion forming the contact portion  31   a  in the contact position adjusting piston  31  are sealed with sealing members. Because other structures are not different from those of the first embodiment, they are provided with the same reference numerals as those of the first embodiment. 
   According to the second embodiment, in a state in which the stop position setting piston  21  has been driven by supplying the pressure fluid from the port  28  to the pressure chamber  27  and the stopper  23  has come in contact with the contact portion  31   a  of the contact position adjusting piston  31 , if the pressure fluid at the same pressure is supplied to the pressure chamber  58  from the port  67  through the rod encapsulating tube  66  and the port  59  at the end portion of the auxiliary rod  22 , fluid pressure also acts on the end face of the auxiliary rod  22  in the rod encapsulating tube  66 . Therefore, fluid pressure operating forces acting on opposite sides of the stop position setting piston  21  and the auxiliary rod  22  become substantially equal to each other. Therefore, the stop position setting piston  21  is not pushed back by the force from the side of the pressure chamber  58 . 
   In the third embodiment in  FIG. 7 , a projecting lever  75  is provided to a stop position setting piston  73 . The projecting lever  75  projects into a pipe  74  forming the main rod  13  through an insertion hole  72  of a main piston  71 . The flow path  60  in the auxiliary rod  22  opens into a pressure chamber  77  between the main piston  71  and the stop position setting piston  73  through a hole  76  provided to the projecting lever  75  and opens into the pipe  74  through a through hole  78  in the projecting lever  75 . A locking member  79  to be locked to a hole edge of the insertion hole  72  of the main piston  71  is provided to a tip end of the projecting lever  75  projecting into the pipe  74 . The projecting lever  75  has substantially the same diameter as the auxiliary rod  22  connected to the stop position setting piston  73  and extending outside on the side of the head cover. 
   With this structure, in a state in which the pressure fluid has been supplied from the port  28  to the pressure chamber  27 , even if the pressure fluid at the same pressure is supplied through the flow path  60  from the hole  76  to the pressure chamber  77  between the stop position setting piston  73  and the main piston  71  and is supplied from the through hole  78  into the pipe  74 , because the locking member  79  is locked to the main piston  71 , the fluid pressure in the pressure chamber  77  does not act as a force for moving the main piston  71  and the stop position setting piston  73  and the fluid pressure in the pipe  74  only acts as a force for pushing back the stop position setting piston  73 . Therefore, the piston  73  is not pushed back. 
   In a fourth embodiment in  FIG. 8 , a projecting lever  85  is provided to a stop position setting piston  83  and the projecting lever  85  is fitted in a sealed state in opposite directions in an insertion hole  82  provided in a main piston  81 . A diameter of the projecting lever  85  is set to be larger than the diameter of the auxiliary rod  22 . The flow path  60  in the auxiliary rod  22  opens through a small hole  86  provided to the projecting lever  85  into a pressure chamber  87  between the main piston  81  and the stop position setting piston  83 . The insertion hole  82  provided to the main piston  81  is connected through a through hole  88  in the main rod  13  to the port  55  opening into a recessed portion  89  in the rod cover  11 . 
   Because of this structure, in the state in which the pressure fluid is supplied from the port  28  to the pressure chamber  27 , even if the pressure fluid at the same pressure is supplied through the flow path  60  to the pressure chamber  87  between the stop position setting piston  83  and the main piston  81  through the small hole  86 , the stop position setting piston  83  is not pushed back because the pressure receiving area of the stop position setting piston  83  facing the pressure chamber  87  is smaller than the pressure receiving area facing the other pressure chamber  27 . 
   When the main piston  81  returns, the stop position setting piston  83  is not pushed back by the returning main piston  81 . In other words, if the compressed air in the pressure chamber  87  is discharged and the compressed air is supplied from the port  55  through the cushion packing  53  and the like to the return-side pressure chamber  54  at the same time, the main piston  81  returns to a position shown in a chain line and comes in contact with the stop position setting piston  83 . At this time, the compressed air also flows into the insertion hole  82  in the main piston  81  through the passage  88 . The compressed air acts in the insertion hole  82  in such a direction as to push back the projecting lever  85  while acting on the main piston  81  in such a direction as to move the main piston  81  forward. Therefore, the operating forces cancel each other and, as a result, air pressure operating forces acting on the main piston  81  and the stop position setting piston  83  are obtained from air pressure supplied to the pressure chamber  87  and the pressure chamber  27 . Here, because the pressure receiving area of the main piston  81  is smaller than the pressure receiving area of the stop position setting piston  83 , the stop position setting piston  83  is not pushed back by the main piston  81 . 
   Because other structures and operations of the third and fourth embodiments are substantially similar to those of the first embodiment, main portions in the drawings are provided with the same reference numerals as those of the first embodiment to omit description of them. 
   The cylinder apparatus in each the above-described embodiment can be used not only as a gun pressurizing device for a welding assembly line of an automobile body, steel furniture, or the like but also as a cylinder of a pressurizing unit in various clamping devices and other cylinders for various uses in which an intermediate stop is required. 
   According to the invention described above in detail, it is possible to provide at a low cost a cylinder apparatus with a simple mechanism by which problems of a prior-art fluid pressure cylinder for a spot welding gun or the like are solved. To put it more concretely, the cylinder apparatus has at least two stages of stop positions with respect to an object and a degree of freedom of a stroke is increased to be adaptable to various kinds of members to be welded. As a result, it is possible to obtain the cylinder apparatus less expensive and with better operability than an electric (servo) welding gun.