Dual stroke cylinder

Abstract

A first piston 13A and a second piston 13B are disposed in a cylinder tube 12A, a hollow piston rod 17 is connected to the second piston 13B, an intermediate stop rod 16 which penetrates the second piston 13B and is fitted into the piston rod 17 is connected to the first piston 13A, a stopper 19 with which the second piston 13B engages is disposed at the tip of the intermediate stop rod 16, and cylinder chambers 14A, 14B and 14C are formed respectively between the first piston 13A and the head cover 12B, between both pistons 13A and 13B, and between the second piston 13B and the rod cover 12C.

Description

TECHNICAL FIELD

The present invention relates to a dual stroke cylinder in which a piston rod can be stopped in an intermediate position of the stroke.

PRIOR ART

A normal hydrostatic pressure cylinder is so constructed that a piston rod thereof moves from the starting end to the termination of the stroke all at once. However, there is a demand according to the operation contents for stopping the piston rod in an intermediate position of the stroke, performing some operations during the stroke up to that position, and moving the piston rod again up to the termination of the stroke to perform an operation for the next stage. Moreover, energization of a solenoid valve for controlling the hydrostatic pressure may be cut off due to an unforeseen situation. In that case, with a normal hydrostatic pressure cylinder, a part of an operator's body may be put between work pieces mounted on the rod, at the starting end or termination of the stroke of the piston rod. As a safety measure for preventing such a problem, it is more effective to use a hydrostatic pressure cylinder which can be stopped in an intermediate position and designate the intermediate stop position as a non-energized origin, than a method using a lock mechanism or a three position valve.

FIG. 6 shows one example of a dual stroke cylinder already proposed by the present applicant, in which a piston rod can be stopped in an intermediate position of the stroke. This dual stroke cylinder 1 comprises: a cylinder tube 2 A, a first piston 3 A sliding airtightly in the cylinder tube 2 A; an annular second piston 3 B sliding airtightly in the cylinder tube 2 A on the rod side of the first piston 3 A; a hollow piston rod 7 integral with the second piston 3 B; a head cover 2 B; and a rod cover 2 C.

Inside the cylinder tube 2 A, there is provided a stopper rod 6 for setting the stroke of the first piston 3 A, which penetrates the center of the first piston 3 A so that it can slide freely and airtightly, with one end thereof being fitted to the head cover 2 B.

Moreover, the hydrostatic pressure cylinder 1 comprises: a first port 5 A for supplying a pressure fluid to a first cylinder chamber 4 A on the head cover 2 B side of the first piston 3 A; a second port 5 B for supplying a pressure fluid to a second cylinder chamber 4 B between the first piston and the second piston via the inside of the stopper rod 6 ; and a third port 5 C for supplying a pressure fluid to a third cylinder chamber 4 C on the rod cover 2 C side of the second piston 3 B.

Therefore, when the pressure fluid is supplied from the first port 5 A to the first cylinder chamber 4 A, the first piston 3 A is driven, and at the same time, the second piston 3 B and the piston rod 7 pushed thereby are driven in the same direction. When the first piston 3 A slides as far as the stopper 6 B located at the termination of the stopper rod 6 , the first piston 3 A stops at a position which is moved to the left by a stroke S 1 in the figure, and then the pushed second piston 3 B and rod 7 stop in the intermediate position of the stroke.

In this state, when the pressure fluid is supplied from the second port 5 B to the second cylinder chamber 4 B between the first piston and the second piston, and if the pressure fluid has been introduced into the third cylinder chamber 4 C, when the pressure fluid is discharged according to need, the second piston 3 B and the rod 7 thereof which are stopped in the intermediate position of the stroke move to the left by the remaining stroke (S 2 -S 1 ) and stop at the termination position of the driving stroke.

This dual stroke cylinder 1 can stop the rod 7 of the second piston 3 B to the intermediate position of the stroke S 2 . However, since the first piston 3 A bumps against the stopper 6 B of the stopper rod 6 at the time of stopping in the intermediate position, the stopper rod 6 undergoes an impact force every time the first piston 3 A is driven.

Accordingly, it is necessary to give strength to the stopper rod 6 so as to endure the impact force. When the strength of the stopper rod 6 is increased, the diameter of the stopper rod 6 increases, and the inner diameter of the first piston 3 A which slides on the outer circumference of the stopper rod 6 also increases. Hence, the area presented to the wind of the first piston 3 A decreases by that amount, causing a problem in that the output of the first piston 3 A decreases.

Furthermore, if the stopper rod 6 is made large, the rigidity of the stopper rod 6 increases, and hence the stopper rod 6 cannot be bent, and as a result, it becomes necessary to strictly adjust the parallelism of the stopper rod 6 and the cylinder tube 2 A.

DISCLOSURE OF THE INVENTION

It is an object of the present invention to solve the problems in the dual stroke cylinder already proposed and to provide a dual stroke cylinder in which a stopper rod is not required.

To achieve the above object, the dual stroke cylinder of the present invention is characterized in that it has: a cylinder tube having a head cover and a rod cover fitted to the opposite ends thereof; first and second two pistons which slide airtightly in the cylinder tube; cylinder chambers respectively partitioned between the first piston and the head cover, between the two pistons, and between the second piston and the rod cover; ports for supplying a pressure fluid respectively to each cylinder chamber; a piston rod with the base end portion being connected to the second piston, and the top end portion penetrating the rod cover airtightly, and extending to the outside of the cylinder tube; a hollow rod for intermediate stop having a stopper at the top end portion, with which the second piston is engaged and stops, with the base end portion being connected to the first piston, and with the top end portion penetrating the second piston so as to be relatively freely movable in the back and forth direction, and going into the inside of the piston rod; a conduit shaft having a fluid passage connecting a hollow portion in the piston rod and the second port inside thereof, with the base end portion being connected to the head cover and airtightly and slidably penetrating the first piston and the rod for intermediate stop, and with the top end portion being located in the hollow portion of the piston rod.

In the present invention, it is preferable to have position adjusting means that can adjust the position of the first piston at a return end along the axis of the piston. This position adjusting means is desirably a bolt screwed into the head cover so as to freely advance and retreat, with the top end protruding into the first cylinder chamber.

In the present invention, the stopper fitted to the top end of said rod for intermediate stop is position-adjustable in the axial direction of the rod for intermediate stop.

In the dual stroke cylinder having the above-described construction, the second piston is slid by means of s pressure fluid supplied from the second port to the second cylinder, and the second piston can be stopped at an intermediate position of the stroke by means of the stopper and the second piston and the rod thereof can be held at that intermediate position. By supplying the pressure fluid from the first port to the first cylinder in that state, the first and second pistons and the piston rod can be moved to the stroke termination position.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a longitudinal elevation view showing a main part in an embodiment of a dual stroke cylinder according to the present invention.

FIG. 2 is a side view on the rod cover side in the embodiment shown in FIG. 1 .

FIG. 3 is a diagram for explaining the operation of the present invention and a schematic sectional view showing a state that a piston rod is located in the termination of the return stroke.

FIG. 4 is a schematic sectional view showing a state that the piston rod is stopped in the intermediate position.

FIG. 5 is a schematic sectional view showing a state that the piston rod is located at the termination in the drive stroke.

FIG. 6 is a schematic sectional view showing one example of a dual stroke cylinder already proposed.

DETAILED DESCRIPTION

FIG. 1 is a longitudinal elevation view showing a main part in an embodiment of a dual stroke cylinder according to the present invention, and FIG. 2 is a side view on the rod side in FIG. 1 . The dual stroke cylinder 11 comprises one cylinder tube 12 A, and first and second pistons 13 A, 13 B that slide airtightly in the cylinder tube 12 A.

The cylinder tube 12 A comprises a head cover 12 B airtightly fitted to one end thereof by means of a retaining ring 23 , and a rod cover 12 C airtightly fixed to the other end thereof by means of a bolt 24 .

In the central portion of the head cover 12 B, there is screwed one end of a hollow shaft 18 extending in the central portion of the cylinder tube 12 A toward the rod cover 12 C, and having an axially penetrating passage 21 in the central portion thereof.

The first piston 13 A airtightly sliding in the cylinder tube 12 A has a tubular rod 16 for intermediate stop extending axially in the central portion thereof. This intermediate stop rod 16 has an external screw portion having a small diameter at the opposite ends, with the one end thereof being screwed airtightly into the central portion of the first piston 13 A, and a stopper 19 comprising a nut being screwed into the other end thereof.

The shaft 18 penetrates inside the first piston 13 A and the intermediate stop rod 16 , a seal member is fitted between the shaft 18 and the first piston 13 A, thereby the first piston 13 A slides airtightly on the outer circumference of the shaft 18 .

Moreover, into the annular second piston 13 B is airtightly screwed a base end portion of an annular piston rod 17 having a hollow portion 17 A, and the intermediate stop rod 16 and the stopper 19 are fitted into the inside of the piston rod 17 so as to be relatively freely movable in the back and forth direction, as well as the shaft 18 being fitted therein. The top end portion of this piston rod 17 penetrates airtightly the rod cover 12 C and reaches outside of the cylinder tube 12 A, and the top end portion thereof is blocked up by a rod block 17 B. The second piston 13 B also comprises an engagement portion 19 A wherein the stroke for intermediate stop is set by means of the engagement with the stopper 19 .

Moreover, a first cylinder chamber 14 A is formed between the head cover 12 B and the first piston 13 A, a second cylinder chamber 14 B communicated with the hollow portion 17 A of the piston rod 17 is formed between the first piston 13 A and the second piston 13 B, and a third cylinder chamber 14 C is formed between the second piston 13 B and the rod cover 12 C.

Then, first, second and third ports 15 A, 15 B and 15 C for supplying compressed air respectively to the first, second and third cylinder chambers 14 A, 14 B and 14 C are established in the cylinder tube 12 A, and of these, the first port 15 A and the third port 15 C are directly communicated with the respectively corresponding cylinder chambers 14 A and 14 C.

On the other hand, the second port 15 B is communicated with the second cylinder chamber 14 B via passages 22 and 21 formed inside the head cover 12 B and the shaft 18 , and the hollow portion 17 A in the piston rod 17 .

A position restriction bolt 25 for restricting the stop position of the first piston 13 A is screwed into the head cover 12 B with the top end thereof airtightly penetrating the head cover 12 B and protruding into the first cylinder chamber 14 A.

A reference symbol 28 C in FIG. 1 denotes a packing material for airtightly sealing between the outer circumference of the piston rod 17 and a central hole in the rod cover 12 C, 29 denotes a bearing, 28 A and 28 B denote packing materials for airtightly sealing, respectively, between the first piston 13 A and the inner circumference of the cylinder tube 12 A and between the second piston 13 B and the inner circumference of the cylinder tube 12 A. A reference symbol 28 D denotes a packing material for airtightly sealing between the first piston 13 A and the outer circumference of the shaft 18 , 20 A denotes a washer disposed on the second piston 13 B in a portion where the stopper 19 engages therewith, 26 denotes a nut for locking the position of the position restriction bolt 25 and 27 denotes a sealing member for airtightly sealing the position restriction bolt 25 .

The position restriction bolt 25 can advance or retreat by loosening the nut 26 , to thereby make the first piston 13 A abutting against the position restriction bolt 25 , the intermediate stop rod 16 and the stopper 19 advance or retreat in the axial direction of the cylinder tube 12 A, thereby enabling adjustment of the intermediate stop position of the piston rod 17 which abuts against the stopper 19 and stops.

Moreover, the intermediate stop position of the piston rod 17 may be adjusted by changing the position of the stopper 19 screwed in the external screw portion of the intermediate stop rod 16 .

In this case, since a passage for supplying compressed air to the second cylinder chamber 14 B between the first piston 13 A and the second piston 13 B is constituted by passages 22 and 21 respectively disposed in the head cover 12 B and the shaft 18 , and the hollow portion 17 A disposed in the piston rod 17 , compressed air can be supplied to the second cylinder chamber 14 B, regardless of the intermediate stop position of the piston rod 17 .

The operation of the above-described embodiment will now be described with reference to FIG. 3 to FIG. 5 .

FIG. 3 shows a condition that compressed air is supplied from the third port 15 C to the third cylinder chamber 14 C, the air in the first and second cylinder chambers 14 A, 14 B are discharged outside respectively from the first and second ports 15 A, 15 B, and the first and second pistons 13 A, 13 B, the intermediate stop rod 16 and the piston rod 17 are at the termination of the return stroke.

In this condition, when the pressure fluid is supplied from the second port 15 B to the second cylinder chamber 14 B between the first piston 13 A and the second piston 13 B, since the area presented to the wind of the second cylinder chamber 14 B is large, the second piston 13 B and the rod 17 thereof are pushed and driven by the pressure fluid.

When the second piston 13 B slides to the position of the stopper 19 , the engagement portion 19 A of the second piston 13 B bumps against the stopper 19 , and hence the second piston 13 B and the rod 17 thereof stop in the intermediate position of the stroke (see FIG. 4 ).

When the second piston 13 B reaches the intermediate stop position, the engagement portion 19 A bumps against the stopper 19 . However, since the pressure fluid in the third cylinder chamber 14 C acting on the second piston 13 B exerts buffer action, the engagement portion 19 A does not bump against the stopper member with a large impact force.

Moreover, the stopper 19 and the first piston 13 A connected thereto are not fixed to the cylinder tube 12 A, and the position is held by the hydrostatic pressure. Hence, when the second piston 13 B bumps against the stopper 19 , the first piston 13 A and the second piston 13 B do not undergo a large impact force due to the buffer action by means of the fluid, and as a result, the strength can be reduced compared to the conventional example in FIG. 6 .

In the above condition, when the pressure fluid is supplied from the first port 15 A to the first cylinder chamber 14 A disposed on the head side of the first piston 13 A, the hydrostatic pressure acts on the first piston 13 A. However, since the area presented to the wind on the both faces in the axial direction of the first piston 13 A is equal, the first piston 13 A is not directly pushed by the pressure fluid in the first cylinder chamber 14 A. However, the second piston 13 B connected to the first piston 13 A via the stopper 19 is pushed by the pressure fluid in the second cylinder chamber 14 B, and the pressure fluid pushing the second piston 13 B in the return direction is only the pressure fluid in the third cylinder chamber 14 C. As a result, the second piston 13 B is driven to the termination of the stroke, together with the first piston 13 A, due to the difference in the area presented to the wind (see FIG. 5 ).

When the second piston 13 B slides so far as the termination of the stroke, the second piston 13 B bumps against the rod cover 12 C, and stops at the termination position of the stroke together with the rod 17 .

In order to return the rod 17 , when the fluid in the first cylinder chamber 14 A is discharged to outside, the first and second pistons 13 A, 13 B and the rod thereof return to the intermediate stop position of the stroke.

Then, when the fluid in the second cylinder chamber 14 B is discharged outside, the second pistons 13 B and the rod thereof move to the termination of the return stroke due to the hydrostatic pressure in the third cylinder chamber 14 C.

If necessary, in the condition of FIG. 5 , if the fluid in the first and second cylinder chambers 14 A, 14 B are discharged outside together, the first and second pistons 13 A, 13 B and the piston rod 17 thereof move to the termination of the return stroke, without stopping in the intermediate position of the stroke, due to the hydrostatic pressure of the third cylinder chamber 14 C.

Moreover, if the position restriction bolt 25 shown in FIG. 1 is made to advance or retreat, the position of the return end of the first piston 13 A abutting against the position restriction bolt 25 , and hence the position of the return end of the stopper 19 are changed, to thereby change the stop position of the second piston 13 B. As a result, the intermediate stop position of the piston rod 17 can be adjusted. In this case, since the pressure fluid is supplied and discharged to/from the second cylinder chamber 14 B by the passages 21 , 22 disposed in the shaft 18 of the hydrostatic pressure cylinder and the head cover 12 B and the hollow portion 17 A disposed in the piston rod, even if the intermediate stop position of the piston rod 17 is adjusted, the second port 15 B for supplying the compressed air to the second cylinder chamber 14 B can be established in a fixed position of the cylinder tube.

With the dual stroke cylinder 11 , since the piston rod 17 can be stopped at the intermediate position of the stroke, it ban be utilized for various applications which require intermediate stop. Also, by designating the intermediate stop position as a non-energizing origin, as a safety measure with respect to a case where energization is stopped due to an unforeseen situation, it can be prevented that a part of an operator's body is put between work pieces in the vicinity of the starting end and the termination of the stroke.

In this case, since the intermediate stop position of the piston rod 17 is held by the engagement portion 19 A of the second piston 13 B abutting against the stopper 19 , the stop position is accurate and retention thereof is secured, compared to the retention of the stop position of a piston rod by means of a lock mechanism or the like.

As described above in detail, according to the dual stroke cylinder of the present invention, the second piston and the piston rod connected thereto can be stopped in the intermediate position of the stroke by the stopper, and at that time, since the stopper and the first piston connected thereto are not fixed to the hydrostatic cylinder and the position thereof is held by the hydrostatic pressure, even if the second piston bumps against the stopper, the first piston and the second piston do not undergo a large impact force.

Moreover, even if the second piston bumps against the stopper, the shaft fitted to the head cover of the hydrostatic cylinder, on the outer circumference of which the first piston airtightly slides, does not undergo the impact force. Therefore, the shaft and the head cover do not require large strength. As a result, the diameter of the shaft can be made small, and the head cover can be designed to be thin.

By making the diameter of the shaft small, the inner diameter of the first piston that slides on the outer circumference of the shaft also becomes small. As a result, the area presented to the wind of the first piston can be increased by that amount, and hence even a hydrostatic cylinder having the same size can increase the output of the first piston.

Also, since the shaft does not undergo the impact force, a flexible pipe can be used as a shaft.

If a flexible pipe is used as the shaft, since it is not necessary to strictly adjust the parallelism of the shaft and the cylinder tube, a dual stroke cylinder having a long stroke can be produced. Also, even if the head cover is fitted to the cylinder tube with a slight inclination, since the shaft is flexible, it does not cause any problem in sliding of the first piston.

According to the dual stroke cylinder of the present invention, the stroke of the second piston established by the stopper can be adjusted, and since the stop position of the second piston changes, the intermediate stop position of the piston rod can be adjusted.

Claims

1. A dual stroke cylinder comprising:a cylinder tube having a head cover and a rod cover fitted to the opposite ends thereof; a first piston on the head cover side and a second piston on the rod cover side which slide airtightly in said cylinder tube, the second piston including a center hole; a first cylinder chamber partitioned between said first piston and said head cover; a second cylinder chamber partitioned between said two pistons; a third cylinder chamber partitioned between said second piston and said rod cover; first, second and third ports for individually supplying pressure fluid respectively to each cylinder chamber; a piston rod having a hollow portion, the piston rod including a piston base end portion being connected to said second piston such that the hollow area communicates with the center hole of the second piston, and a piston top end portion penetrating said rod cover airtightly, extending to the outside of the cylinder tube, and sealed from an exterior of the cylinder tube; a hollow rod for intermediate stop having a stopper at the top end portion, with which said second piston is engaged and stopped at a position of a most advancing end, the stopper providing a gap between the stopper and the second piston, with a rod base end portion being connected to said first piston, and a rod top end portion penetrating said second piston so as to be freely movable in the back and forth direction, and going into the inside of said piston rod; and a conduit shaft having a fluid passage connecting a hollow portion in said piston rod and said second port therein, with a shaft base end portion being connected to said head cover and airtightly and slidably penetrating said first piston and said rod for intermediate stop, and with a shaft top end portion extending into said hollow portion, such that fluid delivered to the second port flows through the stopper gap to the second cylinder chamber.

2. A dual stroke cylinder according to claim 1, having position adjusting means which can adjust the position of said first piston at a return end in the back and forth direction along the axis of said piston.

3. A dual stroke cylinder according to claim 2, wherein said position adjusting means is a bolt screwed into said head cover so as to freely advance and retreat, with a bolt top end protruding into said first cylinder chamber.

4. A dual stroke cylinder according to claim 1, wherein said stopper fitted to the top end of the hollow rod for intermediate stop is position-adjustable in the axial direction of the hollow rod for intermediate stop.