Patent Description:
A fluid pressure cylinder, which is used for, for example, a clamping mechanism and which includes separate cylinders for moving an end of a piston rod to a position adjacent to a workpiece (transfer cylinder) and for performing predetermined tasks on the workpiece using the end of the piston rod (output cylinder), is well known in the art.

For example, an air cylinder described in <CIT> includes a booster cylinder disposed between a pair of drive cylinders. In the air cylinder, while air is supplied to second cylinder chambers of the drive cylinders to cause a booster rod and drive rods to advance, there is little or no difference in pressure between a third cylinder chamber and a fourth cylinder chamber of the booster cylinder, and thus no or little advance thrust acts on the booster rod. When a connector plate connecting the booster rod and the drive rods comes into contact with a workpiece and causes the booster rod and the drive rods to stop, the pressure in first cylinder chambers of the drive cylinders drops, and a valve element of a first valve device is switched to a boost position. This causes the pressure in the third cylinder chamber to be atmospheric while the fourth cylinder chamber is being pressurized, and thereby advance thrust acts on the booster rod.

As a technology related to the present application, document <CIT> discloses a fluid pressure actuated drive for an injection moulding machine which comprises four cylinders. In each of the cylinders, piston rods are respectively connected to one end (right end) and the other end (left end) of the piston. Right and left chambers that are partitioned by the piston are configured to be switched between a state where communication between the right and left chambers is blocked off and a state where the right and left chambers communicate to each other, by rotation of a disc coaxially incorporated in the piston.

In the above-described air cylinder, air needs to be supplied to the first cylinder chambers of the drive cylinders to return the drive rods, placing a limit on the reduction in the air consumption. Moreover, two pipes need to be disposed between the drive cylinders and a switching valve that switches between supplying air to the first cylinder chambers while discharging air from the second cylinder chambers and supplying air to the second cylinder chambers while discharging air from the first cylinder chambers. A fluid pressure cylinder including a piston rod for a transfer cylinder and a piston rod for an output cylinder coaxially connected in series is also well known, and has problems similar to those described above in addition to an undesirable increase in size due to the extended total length.

The present invention has been devised taking into consideration the aforementioned problems, and has the object of providing a compact fluid pressure cylinder including a cylinder portion for transfer and a cylinder portion for output and consuming as little pressurized fluid as possible. The present invention also has the object of providing a fluid pressure cylinder requiring only one connection pipe.

These problems are solved by a fluid pressure cylinder according to claim <NUM>. Preferred embodiments of the invention are provided by the dependent claims.

A fluid pressure cylinder according to the present invention includes: a first cylinder portion and a second cylinder portion disposed in parallel; and a supply-and-discharge port. The first cylinder portion is partitioned by a first piston into a first accumulation chamber disposed on a head side and a second accumulation chamber disposed on a rod side. The second cylinder portion is partitioned by a second piston into a release chamber disposed on the head side and a drive chamber disposed on the rod side. Pressurized fluid is supplied to and discharged from the second accumulation chamber and the drive chamber through the supply-and-discharge port. An end of a first piston rod connected to the first piston and an end of a second piston rod connected to the second piston are connected to each other. The first piston is provided with a communication switching valve configured to switch communication between the first accumulation chamber and the second accumulation chamber, between enabled and disabled. The second accumulation chamber is connected to the supply-and-discharge port via a flow path provided with a check valve, the check valve allowing fluid to flow from the supply-and-discharge port toward the second accumulation chamber and blocking flow of fluid from the second accumulation chamber toward the supply-and-discharge port. During a retraction stroke, pressurized fluid is supplied from a fluid supply source to the drive chamber and the second accumulation chamber while the first accumulation chamber and the second accumulation chamber communicate with each other, whereas, during an extension stroke, pressurized fluid in the drive chamber is discharged while the first accumulation chamber and the second accumulation chamber communicate with each other.

According to the fluid pressure cylinder, pressurized fluid may be supplied to the second cylinder portion configured as a transfer cylinder only when the second piston is moved in one direction (return direction), that is, during the retraction stroke. This reduces the consumption of pressurized fluid to the fullest extent possible. Moreover, the parallel arrangement of the first cylinder portion and the second cylinder portion prevents the fluid pressure cylinder from increasing in size. Furthermore, a pipe connecting to the supply-and-discharge port is the only pipe required to connect to the fluid pressure cylinder. This facilitates pipe routing.

In the fluid pressure cylinder according to the present invention, the first piston in the first cylinder portion configured as an output cylinder can be advanced using the difference between the pressure-receiving areas in the first piston caused by connecting the first accumulation chamber and the second accumulation chamber to each other. That is, the first cylinder portion can function as an advance transfer cylinder, and thus pressurized fluid may be supplied to the second cylinder portion only when the second piston is returned. This ultimately reduces the consumption of pressurized fluid. Moreover, since pressurized fluid is supplied to and discharged from the second accumulation chamber and the drive chamber through the single supply-and-discharge port, only one pipe is required to connect to the fluid pressure cylinder, facilitating pipe routing.

A preferred embodiment of a fluid pressure cylinder according to the present invention will be described in detail below with reference to the accompanying drawings. A fluid pressure cylinder <NUM> is connected to a supply-and-discharge switching valve <NUM> to perform tasks such as positioning of workpieces. Fluid to be used includes pressurized fluid such as compressed air.

As illustrated in <FIG>, <FIG>, and <FIG>, the fluid pressure cylinder <NUM> includes a rectangular parallelepiped cylinder body <NUM> with a first cylinder hole <NUM> and a second cylinder hole <NUM> having a smaller diameter than the first cylinder hole <NUM>. The first cylinder hole <NUM> and the second cylinder hole <NUM> extend from one longitudinal end to the other longitudinal end of the cylinder body <NUM> and are aligned vertically.

One end of the first cylinder hole <NUM> is closed by a first head cover <NUM>, whereas the other end of the first cylinder hole <NUM> is closed by a first rod cover <NUM>. The first cylinder hole <NUM> and a first piston <NUM> slidably disposed inside the first cylinder hole <NUM> constitute a first cylinder portion <NUM>. The first cylinder hole <NUM> is partitioned by the first piston <NUM> into a first accumulation chamber <NUM> adjacent to the first head cover <NUM> (head side) and a second accumulation chamber <NUM> adjacent to the first rod cover <NUM> (rod side). As is clear from the explanation of effects below, the first cylinder portion <NUM> functions as an advance transfer cylinder as well as an output cylinder.

One end of the second cylinder hole <NUM> is closed by a second head cover <NUM>, whereas the other end of the second cylinder hole <NUM> is closed by a second rod cover <NUM>. The second cylinder hole <NUM> and a second piston <NUM> slidably disposed inside the second cylinder hole <NUM> constitute a second cylinder portion <NUM>. The second cylinder hole <NUM> is partitioned by the second piston <NUM> into a release chamber <NUM> adjacent to the second head cover <NUM> (head side) and a drive chamber <NUM> adjacent to the second rod cover <NUM> (rod side). The second cylinder portion <NUM> functions as a return transfer cylinder. The first cylinder portion <NUM> and the second cylinder portion <NUM> are disposed in parallel.

One end part of a first piston rod <NUM> is connected to the first piston <NUM>, whereas the other end part of the first piston rod <NUM> extends to the outside through the first rod cover <NUM>. One end part of a second piston rod <NUM> is connected to the second piston <NUM>, whereas the other end part of the second piston rod <NUM> extends to the outside through the second rod cover <NUM>.

The other end part of the first piston rod <NUM> and the other end part of the second piston rod <NUM> are connected by a rectangular connector plate <NUM>. Specifically, with the other end part of the first piston rod <NUM> fitted in a first insertion hole 52a created in the connector plate <NUM>, an output member <NUM> and a first nut 56a disposed on either side of the first insertion hole 52a are screwed onto the first piston rod <NUM>, thereby securing the first piston rod <NUM> to the connector plate <NUM>. Moreover, with the other end part of the second piston rod <NUM> fitted in a second insertion hole 52b created in the connector plate <NUM>, a second nut 56b and a third nut 56c disposed on either side of the second insertion hole 52b are screwed onto the second piston rod <NUM>, thereby securing the second piston rod <NUM> to the connector plate <NUM>.

In this case, the inside diameter of the first insertion hole 52a is larger than the outside diameter of the first piston rod <NUM>, and the inside diameter of the second insertion hole 52b is larger than the outside diameter of the second piston rod <NUM>. As a result, even if there are production errors and assembly errors, the first piston rod <NUM> and the second piston rod <NUM> can be kept parallel to each other, and sliding resistance of the first piston <NUM> and the second piston <NUM> can thus be reduced. The first piston <NUM> and the second piston <NUM> move in an integrated manner via the first piston rod <NUM>, the connector plate <NUM>, and the second piston rod <NUM>.

In the description below, a stroke in which the first piston <NUM> and the second piston <NUM> move in a direction in which the first piston rod <NUM> and the second piston rod <NUM> are pushed out of the cylinder body <NUM> (advance direction) is referred to as "extension stroke", whereas a stroke in which the first piston <NUM> and the second piston <NUM> move in a direction in which the first piston rod <NUM> and the second piston rod <NUM> are pulled into the cylinder body <NUM> (return direction) is referred to as "retraction stroke". The fluid pressure cylinder <NUM> performs tasks when the output member <NUM> is pushed out integrally with the first piston rod <NUM>.

As illustrated in <FIG> and <FIG>, a supply-and-discharge port <NUM> and a release port <NUM> are created in the top surface of the cylinder body <NUM>. The supply-and-discharge port <NUM> is connected to the supply-and-discharge switching valve <NUM> via a pipe <NUM> (see <FIG>). The release port <NUM> is exposed to the atmosphere.

The cylinder body <NUM> includes a first flow path 14a connecting the second accumulation chamber <NUM> to the supply-and-discharge port <NUM>, a second flow path 14b connecting the drive chamber <NUM> to the supply-and-discharge port <NUM>, and a third flow path 14c connecting the release chamber <NUM> to the release port <NUM> (see <FIG>). A check valve 14e is disposed on the first flow path 14a. The check valve 14e allows fluid to flow from the supply-and-discharge switching valve <NUM> toward the second accumulation chamber <NUM> and blocks flow of fluid from the second accumulation chamber <NUM> toward the supply-and-discharge switching valve <NUM>. The cylinder body <NUM> further includes a fourth flow path 14d connecting a radial path <NUM> in a discharge switching valve <NUM> (described below) to the supply-and-discharge port <NUM>. Part of the first flow path 14a and part of the fourth flow path 14d are illustrated in <FIG>.

The first piston <NUM> is provided with a communication switching valve <NUM> for switching communication between the first accumulation chamber <NUM> and the second accumulation chamber <NUM>, between enabled and disabled. The communication switching valve <NUM> includes a first push rod <NUM> protruding toward the inside of the second accumulation chamber <NUM>.

As illustrated in <FIG>, the first push rod <NUM> is slidably supported inside a guide hole <NUM> passing through the first piston <NUM> in the axial direction. The first push rod <NUM> includes a communication path <NUM> for connecting the first accumulation chamber <NUM> and the second accumulation chamber <NUM> to each other. The communication path <NUM> includes a first hole portion 64a passing through the first push rod <NUM> in a radial direction, and a second hole portion 64b branching off from a point in the first hole portion 64a to extend toward the first accumulation chamber <NUM>. Both ends of the first hole portion 64a are open to an annular gap <NUM> left between the outer circumference of the first push rod <NUM> and the wall surface of the guide hole <NUM>, whereas the end of the second hole portion 64b communicates with the first accumulation chamber <NUM>. When the first push rod <NUM> protrudes toward the inside of the second accumulation chamber <NUM> by a predetermined length or more, the annular gap <NUM> communicates with the second accumulation chamber <NUM>.

The first push rod <NUM> is biased in a direction of protruding toward the inside of the second accumulation chamber <NUM>, by a coil spring <NUM> disposed between the first push rod <NUM> and a spring seat <NUM> secured to the first piston <NUM>. The first push rod <NUM> includes a shoulder 60a that engages with a shoulder 62a provided for the guide hole <NUM>. This engagement limits the protruding length of the first push rod <NUM> and prevents the first push rod <NUM> from coming off. Note that the spring seat <NUM> has a hole 72a in the center.

Near the end of the extension stroke, the first push rod <NUM> comes into contact with the first rod cover <NUM>, is pushed in against the biasing force of the coil spring <NUM>, and slides inside the guide hole <NUM>. When the first push rod <NUM> is pushed in, a packing <NUM> attached to the outer circumference of the first push rod <NUM> comes into contact with the wall surface of the guide hole <NUM> and blocks the communication between the annular gap <NUM> and the second accumulation chamber <NUM>. That is, the communication switching valve <NUM> blocks the communication between the first accumulation chamber <NUM> and the second accumulation chamber <NUM> near the end of the extension stroke. The first push rod <NUM> can be pushed in to a position where the first push rod <NUM> does not protrude from the end face of the first piston <NUM>.

The first rod cover <NUM> is provided with the discharge switching valve <NUM> that switches connection of the second accumulation chamber <NUM> to the supply-and-discharge switching valve <NUM> between enabled and disabled to allow pressurized fluid inside the second accumulation chamber <NUM> to be discharged. The discharge switching valve <NUM> includes a second push rod <NUM> protruding toward the inside of the second accumulation chamber <NUM>. When viewed in the direction along the axis of the first piston rod <NUM>, the first push rod <NUM> of the communication switching valve <NUM> and the second push rod <NUM> of the discharge switching valve <NUM> are separated from the axis in the opposite directions (<NUM> degrees opposite to each other) by an equal distance.

As illustrated in <FIG>, the second push rod <NUM> is slidably supported inside a guide hole <NUM> passing through the first rod cover <NUM> in the axial direction. The guide hole <NUM> in the first rod cover <NUM> includes a small-diameter hole portion 78a adjacent to the second accumulation chamber <NUM>, and a large-diameter hole portion 78b away from the second accumulation chamber <NUM>. The second push rod <NUM> includes a small-diameter shaft portion 76a fitted in the small-diameter hole portion 78a, and a large-diameter shaft portion 76b fitted in the large-diameter hole portion 78b. O-rings 82a and 82b are attached to the outer circumferences of the small-diameter shaft portion 76a and the large-diameter shaft portion 76b, respectively.

The second push rod <NUM> is biased in a direction in which the small-diameter shaft portion 76a protrudes toward the inside of the second accumulation chamber <NUM>, by a coil spring <NUM> disposed between the second push rod <NUM> and a spring seat <NUM> secured to the first rod cover <NUM>. The protruding length of the second push rod <NUM> is limited by engagement of a shoulder 76c formed between the small-diameter shaft portion 76a and the large-diameter shaft portion 76b with a shoulder 78c formed between the small-diameter hole portion 78a and the large-diameter hole portion 78b.

The first rod cover <NUM> includes the radial path <NUM> having one end opened in the outer circumferential surface of the first rod cover <NUM>, and the other end opened in the large-diameter hole portion 78b. As described above, the radial path <NUM> communicates with the fourth flow path 14d in the cylinder body <NUM>. The second push rod <NUM> includes a discharge path <NUM> for connecting the second accumulation chamber <NUM> and the radial path <NUM> to each other. The discharge path <NUM> includes a first hole portion 88a passing through the small-diameter shaft portion 76a of the second push rod <NUM> in a radial direction, and a second hole portion 88b crossing the first hole portion 88a and passing through the second push rod <NUM> in the axial direction.

Near the end of the extension stroke, the second push rod <NUM> comes into contact with the first piston <NUM>, is pushed in against the biasing force of the coil spring <NUM>, and slides inside the guide hole <NUM>. When the second push rod <NUM> is pushed in, the O-ring 82a attached to the small-diameter shaft portion 76a is separated from the wall surface of the small-diameter hole portion 78a, and the second accumulation chamber <NUM> communicates with the radial path <NUM> in the first rod cover <NUM> via the discharge path <NUM> in the second push rod <NUM>. As a result, the second accumulation chamber <NUM> is connected to the supply-and-discharge switching valve <NUM> via the discharge path <NUM>, the radial path <NUM>, the fourth flow path 14d, and the supply-and-discharge port <NUM>. That is, the discharge switching valve <NUM> connects the second accumulation chamber <NUM> to the supply-and-discharge switching valve <NUM> near the end of the extension stroke. The second push rod <NUM> can be pushed in to a position where the second push rod <NUM> does not protrude from the end face of the first rod cover <NUM>.

As illustrated in <FIG>, the supply-and-discharge switching valve <NUM> is configured as a <NUM>-port, <NUM>-position switching valve provided with a first port 92a to a third port 92c and switchable between a first position and a second position. The first port 92a is connected to the supply-and-discharge port <NUM> in the cylinder body <NUM> via the pipe <NUM>. The second port 92b is connected to a fluid supply source (compressor) <NUM>. The third port 92c is connected to a discharge port <NUM> provided with a silencer <NUM>. The first port 92a is connected to the second port 92b when the supply-and-discharge switching valve <NUM> is in the first position, and the first port 92a is connected to the third port 92c when the supply-and-discharge switching valve <NUM> is in the second position. The pipe <NUM> is the only pipe required to connect the fluid pressure cylinder <NUM> and the supply-and-discharge switching valve <NUM>.

The fluid pressure cylinder <NUM> according to this embodiment is basically configured as above. Next, the effects thereof will be described. In <FIG>, long dashed double-short dashed lines indicate the outline of the cylinder body <NUM>.

A state where the first piston <NUM> is disposed in the middle between the first head cover <NUM> and the first rod cover <NUM> as illustrated in <FIG> while the pressures in the first accumulation chamber <NUM>, the second accumulation chamber <NUM>, the drive chamber <NUM>, and the release chamber <NUM> are equal to atmospheric pressure is defined as an initial state.

In this initial state, the supply-and-discharge switching valve <NUM> is in the second position, and thus the supply-and-discharge port <NUM> is connected to the discharge port <NUM>. In addition, the first push rod <NUM> of the communication switching valve <NUM> and the second push rod <NUM> of the discharge switching valve <NUM> protrude toward the inside of the second accumulation chamber <NUM>. Thus, the first accumulation chamber <NUM> and the second accumulation chamber <NUM> communicate with each other, and the connection between the second accumulation chamber <NUM> and the supply-and-discharge switching valve <NUM> through the fourth flow path 14d is blocked.

When the supply-and-discharge switching valve <NUM> is switched to the first position from the initial state, the supply-and-discharge port <NUM> is connected to the fluid supply source <NUM>. Pressurized fluid from the fluid supply source <NUM> is supplied to the drive chamber <NUM> through the supply-and-discharge port <NUM> and the second flow path 14b and to the second accumulation chamber <NUM> through the supply-and-discharge port <NUM> and the first flow path 14a on which the check valve 14e is disposed. When pressurized fluid is supplied to the drive chamber <NUM>, the second piston <NUM> is driven toward the second head cover <NUM>. The first piston <NUM> is also driven toward the first head cover <NUM> in an integrated manner with the second piston <NUM>.

In contrast, pressurized fluid supplied to the second accumulation chamber <NUM> is accumulated in the second accumulation chamber <NUM> and, additionally, in the first accumulation chamber <NUM> communicating with the second accumulation chamber <NUM>. The first piston rod <NUM> and the second piston rod <NUM> are pulled in to the fullest extent possible, and high-pressure fluid is accumulated in the first accumulation chamber <NUM> and the second accumulation chamber <NUM> while the pressures in the accumulation chambers are kept equal (see <FIG>). At this moment, the second piston <NUM> is in contact with the second head cover <NUM>, whereas the first piston <NUM> is not in contact with the first head cover <NUM>.

Next, when the supply-and-discharge switching valve <NUM> is switched to the second position, the supply-and-discharge port <NUM> is connected to the discharge port <NUM>. Pressurized fluid in the drive chamber <NUM> passes through the second flow path 14b, the supply-and-discharge port <NUM>, and the supply-and-discharge switching valve <NUM> and is then discharged from the discharge port <NUM> to the outside. The pressure in the drive chamber <NUM> decreases to atmospheric pressure equal to the pressure in the release chamber <NUM>, and the driving force acting on the second piston <NUM> becomes zero.

In contrast, pressurized fluid in the second accumulation chamber <NUM> is not discharged due to the effect of the check valve 14e. The pressure of fluid accumulated in the first accumulation chamber <NUM> and the pressure of fluid accumulated in the second accumulation chamber <NUM> (the pressures being equal to each other) act on the first piston <NUM> with a difference of an area corresponding to the cross-section of the first piston rod <NUM>. Thus, the force generated by the fluid pressure in the first accumulation chamber <NUM> and pushing the first piston <NUM> toward the first rod cover <NUM> exceeds the force generated by the fluid pressure in the second accumulation chamber <NUM> and pushing the first piston <NUM> toward the first head cover <NUM>. As a result, the first piston <NUM> is driven toward the first rod cover <NUM>; that is, the extension stroke starts (see <FIG>).

In this manner, no pressurized fluid is supplied from the fluid supply source <NUM> to the fluid pressure cylinder <NUM> to start the extension stroke. Subsequently, near the end of the extension stroke, the first push rod <NUM> of the communication switching valve <NUM> comes into contact with the first rod cover <NUM>, while the second push rod <NUM> of the discharge switching valve <NUM> comes into contact with the first piston <NUM>. This blocks the communication between the first accumulation chamber <NUM> and the second accumulation chamber <NUM> and connects the second accumulation chamber <NUM> to the supply-and-discharge switching valve <NUM> via the fourth flow path 14d (see <FIG>).

Pressurized fluid accumulated in the second accumulation chamber <NUM> passes through the fourth flow path 14d, the supply-and-discharge port <NUM>, and the supply-and-discharge switching valve <NUM> in the second position and is then discharged from the discharge port <NUM> to the outside. Pressurized fluid accumulated in the first accumulation chamber <NUM> is prevented from flowing into the second accumulation chamber <NUM> and remains in the first accumulation chamber <NUM>. As a result, the fluid pressure in the first accumulation chamber <NUM> significantly exceeds the fluid pressure in the second accumulation chamber <NUM>, and the first piston <NUM> is pushed toward the first rod cover <NUM> with a large thrust. That is, the fluid pressure cylinder <NUM> produces the maximum force at the end of the extension stroke.

The volume of the second accumulation chamber <NUM> is small near the end of the extension stroke, and only a small amount of pressurized fluid remaining in the second accumulation chamber <NUM> is discharged. Thus, the amount of pressurized fluid supplied to the second accumulation chamber <NUM> during the next retraction stroke may be as small as the amount of discharged fluid.

The first push rod <NUM> brought into contact with the first rod cover <NUM> to receive the reaction force near the end of the extension stroke exerts a force on the first piston <NUM> via the coil spring <NUM>. Moreover, the second push rod <NUM> supported by the first rod cover <NUM> via the coil spring <NUM> also comes into contact with the first piston <NUM> to exert a force in the same direction as above. Since these forces act on the positions separated from the axis of the first piston rod <NUM> in the opposite directions by an equal distance, equalizing the forces by, for example, adjusting the spring constants of the coil spring <NUM> and the coil spring <NUM> can prevent moment causing the first piston <NUM> to be inclined.

Next, when the supply-and-discharge switching valve <NUM> is switched to the first position, pressurized fluid from the fluid supply source <NUM> passes through the supply-and-discharge switching valve <NUM> and is supplied to the drive chamber <NUM> through the supply-and-discharge port <NUM> and the second flow path 14b and to the second accumulation chamber <NUM> through the supply-and-discharge port <NUM> and the first flow path 14a on which the check valve 14e is disposed. As a result, the second piston <NUM> is driven toward the second head cover <NUM> while the first piston <NUM> is driven toward the first head cover <NUM>; that is, the retraction stroke starts (see <FIG>).

When the retraction stroke starts, the first push rod <NUM> of the communication switching valve <NUM> protrudes from the first piston <NUM> by the biasing force of the coil spring <NUM>, and then is separated from the first rod cover <NUM>. At the same time, the second push rod <NUM> of the discharge switching valve <NUM> protrudes from the first rod cover <NUM> by the biasing force of the coil spring <NUM>, and then is separated from the first piston <NUM>. Since the first push rod <NUM> protrudes from the first piston <NUM>, the first accumulation chamber <NUM> and the second accumulation chamber <NUM> communicate with each other. Since the second push rod <NUM> protrudes from the first rod cover <NUM>, the connection between the second accumulation chamber <NUM> and the supply-and-discharge switching valve <NUM> through the fourth flow path 14d is blocked. However, pressurized fluid continues to flow from the supply-and-discharge switching valve <NUM> to the second accumulation chamber <NUM> through the first flow path 14a.

As a result, pressurized fluid from the fluid supply source <NUM> is supplied to the drive chamber <NUM> and supplied to and accumulated in the second accumulation chamber <NUM> via the first flow path 14a. The pressurized fluid is then supplied to and accumulated in the first accumulation chamber <NUM> through the communication switching valve <NUM>. As the retraction stroke proceeds, the second piston <NUM> comes into contact with the second head cover <NUM>. The first piston rod <NUM> and the second piston rod <NUM> are pulled in to the fullest extent possible (see <FIG>), and high-pressure fluid is accumulated in the first accumulation chamber <NUM> and the second accumulation chamber <NUM> while the pressures in the accumulation chambers are kept equal.

From this point forward, the extension stroke performed by switching the supply-and-discharge switching valve <NUM> to the second position and the retraction stroke performed by switching the supply-and-discharge switching valve <NUM> to the first position are repeated. Note that the difference between the cross-sectional areas of the second piston <NUM> and the second piston rod <NUM> is larger than the cross-sectional area of the first piston rod <NUM> to enable the retraction movement when pressurized fluid from the fluid supply source <NUM> is supplied to the drive chamber <NUM> and the second accumulation chamber <NUM> communicating with the first accumulation chamber <NUM>.

In accordance with the fluid pressure cylinder <NUM> according to this embodiment, the first piston <NUM> in the first cylinder portion <NUM> can be advanced using the difference between the pressure-receiving areas in the first piston <NUM>. That is, the first cylinder portion <NUM> can function as an advance transfer cylinder, and thus pressurized fluid may be supplied to the second cylinder portion <NUM> only when the second piston <NUM> is returned. This ultimately reduces the consumption of pressurized fluid.

Pressurized fluid from the fluid supply source <NUM> can be supplied to and discharged from the second accumulation chamber <NUM> and the drive chamber <NUM> through the single supply-and-discharge port <NUM>. That is, the pipe <NUM> is the only pipe required to connect to the fluid pressure cylinder <NUM>. This facilitates pipe routing.

At the end of the extension stroke, pressurized fluid accumulated in the second accumulation chamber <NUM> is discharged while the communication between the first accumulation chamber <NUM> and the second accumulation chamber <NUM> is blocked. As a result, the fluid pressure cylinder <NUM> can exert the maximum force on workpieces.

The first cylinder portion <NUM> functioning as both an output cylinder and an advance transfer cylinder and the second cylinder portion <NUM> functioning as a return transfer cylinder are combined in a parallel arrangement. Thus, the total length of the fluid pressure cylinder <NUM> can be significantly reduced compared with a case where a transfer cylinder and an output cylinder are arranged in series.

The supply-and-discharge switching valve <NUM> connected to the supply-and-discharge port <NUM> can be configured as a <NUM>-port, <NUM>-position switching valve. As a result, the structure of the supply-and-discharge switching valve <NUM> can be simplified.

Claim 1:
A fluid pressure cylinder (<NUM>) comprising:
a first cylinder portion (<NUM>) partitioned by a first piston (<NUM>) into a first accumulation chamber (<NUM>) disposed on a head side and a second accumulation chamber (<NUM>) disposed on a rod side;
a second cylinder portion (<NUM>) partitioned by a second piston (<NUM>) into a release chamber (<NUM>) disposed on the head side and a drive chamber (<NUM>) disposed on the rod side; and
a supply-and-discharge port (<NUM>) through which pressurized fluid is supplied to and discharged from the second accumulation chamber (<NUM>) and the drive chamber (<NUM>), wherein:
the first cylinder portion (<NUM>) and the second cylinder portion (<NUM>) are disposed in parallel;
an end of a first piston rod (<NUM>) connected to the first piston (<NUM>) and an end of a second piston rod (<NUM>) connected to the second piston (<NUM>) are connected to each other;
the first piston (<NUM>) is provided with a communication switching valve (<NUM>) configured to switch communication between the first accumulation chamber (<NUM>) and the second accumulation chamber (<NUM>), between enabled and disabled;
characterized in that
the second accumulation chamber (<NUM>) is connected to the supply-and-discharge port (<NUM>) via a flow path (14a) provided with a check valve (14e), the check valve (14e) allowing fluid to flow from the supply-and-discharge port (<NUM>) toward the second accumulation chamber (<NUM>) and blocking flow of fluid from the second accumulation chamber (<NUM>) toward the supply-and-discharge port (<NUM>).