JPH01131308A - Hydraulic cylinder - Google Patents

Abstract

PURPOSE:To improve the starting property of a hydraulic cylinder and to position its parts accurately by holding and sealing a piston and a piston rod by a fluid film formed between a cylinder tube and a cover. CONSTITUTION:Housing recess portions 13, 17 are formed on a piston 2 and the piston rod holding portion in one side cover 4a and fluid film forming portions 14, 18 are arranged in the housing recess portions 13, 17. Accordingly, sliding resistance between the piston 2 and the inside face of a cylinder tube 1, and that between a piston rod 3 and a sealing member relating thereto become remarkably small so that starting becomes easy and also accurate positioning can be made even at a low speed.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention provides a desired effect on a piston rod connected to a piston by supplying and discharging a pressurized working medium into a space defined by a cylinder tube and a piston. This relates to a fluid pressure cylinder that can provide reciprocating motion.

(Prior art and its problems) A fluid pressure cylinder is an actuator that converts the energy given to a working fluid into linear mechanical motion, and changes the output and speed by controlling the pressure and flow rate of the working fluid. Since it can be easily modified, it is applied to various devices.

As shown in FIG. 5, such a known fluid pressure cylinder usually has a piston 2 slidably disposed in a cylinder tube 1 having a cylindrical inner surface, and a piston 2 is disposed in the cylinder tube 1. A rod 3 is fixed to the cylinder tube, and a cover 4 as a sealing member for sealing the opening of the cylinder tube is integrally fixed to the end of the cylinder tube. Note that each cover 4a, 4b has a cylinder tube l.
Each chamber 5 (only one side is shown in the figure) defined by the piston 2 and the piston 2 is provided with supply and discharge holes 6a and 6b for supplying and discharging a working medium such as pressurized air, etc. .

Here, in order to move the piston rod 3 in the direction shown by arrow A in the figure, the working medium is introduced into the related chamber 5 through the supply/discharge hole 6a, and from the related chamber 5 through the supply/discharge hole 6b. All you have to do is drain the working medium.

Note that the figure shows a state in which the piston 2 has been moved to the end position on the cover 4b side. On the other hand, when it is desired to move the piston rod 3 in the direction opposite to the arrow A, the working medium is guided to the relevant chamber through the supply/discharge hole 6b, while the working medium is discharged through the other supply/discharge hole 6a. Just do it.

By the way, in a fluid pressure cylinder generally having the above-mentioned configuration, the piston 2 disposed within the cylinder tube
In order to slide on the inner surface of the tube and to block mutual communication of the working medium in the chamber 5 separated by the piston, a piston ring as a sealing member 7 is installed in a groove formed in the circumferential direction on the outer periphery of the piston ring. - A ring or the like was buried, or as shown in FIG. 6, a bowl-shaped packing 8 was fixed to the piston body 2a with a bolt 10 via a retainer ring 9.

For this reason, in a fluid pressure cylinder equipped with an O-ring around the outer periphery of the piston as shown in Figure 5, the O-ring rubs against the inner surface of the cylinder tube when the piston moves, resulting in increased sliding resistance. When the pressure of the medium is low, there is a problem in that the piston and piston rod cannot be correctly moved to the desired position. This problem is particularly noticeable when it is desired to maintain the piston in an intermediate position. In order to deal with this problem, it is conceivable to set a relatively large gap between the piston and the inner surface of the cylinder tube, but this tends to cause the 0-ring to deform, and the 0-ring is placed in that gap. Another drawback is that some parts of the blade can be bitten and damaged.

On the other hand, as shown in Fig. 6, in a fluid pressure cylinder using a piston with a piston ring or a bowl-shaped packing, the inner surface of the cylinder tube is ground or honed to reduce the sliding resistance of the piston due to these packings. This caused the problem of increased processing costs.

In addition, in such a sealing member, the gap between the piston and the inner surface of the cylinder tube is inevitably set small, making it susceptible to dust contained in the working medium and even heat. , there is also the problem that its operation becomes unstable.

The present invention has been made in view of such problems,
It is an object of the present invention to provide a hydraulically operated cylinder that can reduce resistance in a piston sliding part and accurately position a piston and, by extension, a piston rod, even in relatively low-speed operating conditions.

(Disclosure of the Invention) In order to achieve this object, the fluid pressure cylinder of the present invention includes a cylinder tube, a piston slidably disposed within the cylinder tube, a piston rod fixed to the piston, and a cylinder tube. a sealing member for sealing the open end of the piston, and a fluid film forming portion made of a fluid-permeable material is provided on the outer periphery of the piston, and at least one sealing member that guides and supports the cylinder tube is provided with a fluid permeable member. Further, the piston rod and the sealing member are provided with supply holes for introducing pressurized fluid to the fluid film forming parts.

(Function) According to this fluid pressure cylinder, when pressurized fluid is supplied to each related fluid film forming part through each supply hole, the pressurized fluid passes through the fluid permeable material and is ejected outward. A thin film of pressurized fluid is formed between the piston and the inner surface of the cylinder tube, and between the piston rod and the sealing member with which the piston rod is associated, to support the piston and the piston rod. Therefore, the sliding resistance between the piston and the inner surface of the cylinder tube, as well as between the piston rod and the associated sealing member, is extremely low, making starting not only easy but also accurate positioning even at low speeds. can do.

(Example) Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a partially omitted cross-sectional view of a preferred embodiment of the hydraulic cylinder of the present invention, and portions in the figure that are equivalent to those shown in FIG. 5 are designated by the same reference numerals.

1 is a cylinder tube, 2 is a piston, 3 is a piston rod, and 4a and 4b are covers as sealing members, respectively.

The piston 2 has a through hole 11 provided therethrough.
are formed, and the piston 2 is connected to the piston rod 3 by fastening a nut to a male thread formed at one end of the piston rod 3 that extends through the through holes 11.
is integrally fixed to.

Further, the piston 2 has a pocket 12 with a larger diameter than the through hole 11 in the middle part, and a pocket 12 on the outer periphery of the pocket 12.
A housing recess 13 communicating with the housing 2 is formed.

The accommodation recesses may extend over the entire circumference of the piston 12, or may be provided at appropriate intervals in the circumferential direction.

The accommodation recess 13 is made of a fluid-permeable material that can freely pass through fluids such as air, water, oil, and gas, such as a ceramic porous body with a three-dimensional network structure that has been specially treated ( A fluid film forming portion 14 made of Press Knight (trade name) and formed into a shape that fits the accommodation recess 13 is attached.

The piston rod 3 connected to the piston is provided with a supply hole 15 that opens into the pocket 12 at one end, opens outward from the piston rod at the other end, and extends substantially in the axial direction of the piston rod. Therefore, when pressurized fluid is supplied from the outer opening, the pressure of the pressurized fluid ejected from the pocket opening decreases in pressure within the pocket 12, flows outward from the fluid film forming part 14, and its static A fluid film of approximately equal pressure is formed in the gap between the piston and the cylinder tube to support and seal the piston.

In this embodiment, which supports the piston rod 3 in a slidable manner, a pocket 16 and an accommodation recess 17 communicating with the pocket 16 are also formed in the piston rod support portion of the cover 48 on one side. This housing recess is provided with another fluid film forming part 18 made of a fluid-permeable material and formed in a shape that fits the housing recess. The fluid film forming portion is fixed by screwing in an annular locking member 20 having a threaded portion that engages with the female thread portion and having an inner diameter larger than that of the piston rod 3.

Furthermore, the cover 48 is provided with a means for supplying pressurized fluid to the pocket 16 (another supply hole 21 is formed in communication with the pocket.
The pressurized fluid that has flowed into 1 flows out from the fluid film forming portion 18 toward the circumferential surface of the piston rod, and forms a fluid film with a pressure approximately equal to the static pressure of the pressurized fluid in the gap between the piston rod and the cover. The piston rod is formed to support the piston rod and to seal it.

Next, the operation of the fluid pressure cylinder of the present invention will be explained with reference to FIG. FIG. 2 schematically shows a positioning device using a fluid pressure cylinder of the present invention, and each supply/discharge port 6a, 6b of the cylinder 25 has a pair of electromagnetic flow control valves that operate in opposite directions. A suitable operating pressure source, such as an air compressor 27, is connected via servo valves 26a and 26b, which can supply pressurized fluid at a desired pressure by adjusting the inflow and outflow of pressurized fluid.
A conduit 28 connected to is connected. Further, an air compressor 27 is similarly connected to each supply hole via a conduit 29. Note that the reference numeral 30 is a regulator that absorbs the pulsation of the compressed air sent from the air compressor 27 and maintains it at a constant pressure.

A table 31 is connected to the piston rod 3 of the cylinder 25. For example, a linear encoder 32 as a position detecting means is arranged in association with this table 31, and a detection signal from the encoder 32 is compared with a position setting signal from a position setting means (not shown) by an arithmetic processing means 33. It is processed and becomes a control signal, which controls each servo valve.

Therefore, the arithmetic processing means adjusts the opening degree of each servo valve based on the position setting signal from the position setting means, and supplies compressed air as a working medium from the air compressor 27 to one chamber 5 of the fluid pressure cylinder 25. Then, the table 31 will be moved to the installed position. At this time, the piston and piston rod are supported and sealed by a fluid film of compressed air supplied from the air compressor as the operating pressure source, so their movement is extremely smooth even at low speeds. As a result, the table can be moved smoothly. Note that the supply of compressed air is continued until there is no difference between the position setting signal and the detection signal from the linear encoder. In this embodiment, the compressed air from the air compressor 27 is guided through the regulator 30 and the conduit 29 to the fluid film forming section 18 through the supply hole 21, but the compressed air is introduced through the servo valve 26a. A portion of the compressed air guided to the port 6a is supplied to the supply hole 2.
In this case, there is an advantage that the pressure difference between the chamber 5 and the fluid film forming portion 18 becomes substantially (or even extremely small).

At this time, compressed air flows out from the fluid film forming part and seals the pipes between the chambers located on both sides of the piston, flows into each chamber 5 of the fluid pressure cylinder, moves the piston, and in turn moves the table 31. It is possible to do so, but
Linear encoder 32 provided in association with table 31
Since the arithmetic processing means 33 adjusts the servo valves 26a and 26b based on the detection signal and position setting signal from the
There is no risk that the table 31 will shift from the predetermined position, and it can be positioned accurately.

Next, FIG. 3 shows another embodiment of the fluid pressure cylinder of the present invention, partially cut away. This embodiment has the same structure as the double-acting cylinder shown in FIG. 1, except for the piston 2. In the fluid pressure cylinder shown in FIG. 1, pressurized fluid, such as compressed air, ejected from the fluid film forming portion 14 toward the inner wall of the cylinder tube 1 is ejected from the gap between the fluid film forming portion 14 and the inner wall of the cylinder tube 1. The compressed air flows into the chamber 5 through the compressed air, and when the fluid pressure cylinder is continuously used, extra compressed air is consumed. Therefore, in the embodiment shown in FIG. 3, in order to prevent the loss caused by the outflow of compressed air from the gap without impairing the sliding movement of the piston 2 along the inner wall of the cylinder tube 1, the piston 2 is
Seal portions 2a are provided at both ends of the shaft, extending in the axial direction thereof.

In this embodiment, the seal portion 2a is a labyrinth seal in which fins forming a small gap and enlarged chambers adjacent to the groove are alternately provided between the seal portion 2a and the inner wall 1a of the cylinder tube.

By providing such seals at both ends of the piston, the blowout of compressed air from the gap between the inner wall of the cylinder tube l and the piston 2 can be reduced to about 1/10 or less compared to the case where these seals are not provided. Not only this, but also the piston 2 can be stably held by the air film formed there, and the movement of the piston can be made even smoother.

Of course, the seal portion is not limited to this labyrinth seal, and may be any seal that allows relative movement between the cylinder and piston and substantially reduces or prevents the flow of pressurized fluid from the gap between them. It is fine as long as it can be done.

FIG. 4 is a partially cutaway view showing another embodiment of the fluid pressure cylinder of the present invention. This embodiment shows a single-acting fluid pressure cylinder, unlike the double-acting type shown in FIG. 1, except that there is no supply/discharge hole 6a and the associated chamber 5. It has almost the same configuration as the embodiment.

If its operation is indicated, the same pressurized fluid as the working medium is supplied to the supply hole 1.
5.21 to the respective fluid film forming portions 14 and 18, while supplying the working medium to the chambers through the supply/discharge port 6b, the piston rod 2, which also functions as a piston, can be moved as indicated by the arrow 3 in the figure. It can be moved smoothly in the direction shown.

Although the present invention has been described above based on the above-mentioned embodiments, the present invention is not limited to these embodiments. Oil, water, etc. can be used as the working medium, and the present invention can also be used as a double rod type cylinder. However, various modifications may be made within the scope of the claims.

(Effects of the Invention) Therefore, according to the fluid pressure cylinder of the present invention, since the piston and piston rod that perform sliding movement are supported and sealed by the fluid film formed between the cylinder tube and the cover, The sliding resistance caused by these is extremely small compared to conventional cylinders, so the starting characteristics are excellent and positioning can be performed with high precision. Moreover, since it is supported by a fluid film, it is not affected by the surface roughness of the inner surface of the cylinder tube, and its processing becomes easy. Moreover, by providing the seal portions at both ends of the piston, the amount of pressurized fluid ejected through the fluid film forming portion of the piston can be reduced, and the piston can be reliably supported by the fluid film. ,
It has many advantages such as smooth operation and reduced running costs.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing an embodiment of the fluid pressure cylinder of the present invention, FIG. 2 is a diagram schematically showing a positioning device using the fluid pressure cylinder shown in FIG. 1, and FIG. 3 is a diagram showing an example of the present invention. FIG. 4 is a cross-sectional view showing another example of the fluid pressure cylinder of the present invention; FIG. 5 is a cross-sectional view showing a conventional hydraulic cylinder. , FIG. 6 is a diagram showing a piston part applied to a conventional fluid pressure cylinder.

Claims (1)

[Scope of Claims] 1. A cylinder tube, a piston that is slidably disposed within the cylinder tube and has a fluid film forming portion made of a fluid permeable material on its outer periphery, and the fluid film forming portion is fixed to the piston. A sealing member having a piston rod having a supply hole for supplying pressurized fluid to the cylinder tube, and another fluid film forming part made of a fluid permeable material provided at each end of the cylinder tube and supporting the piston rod on at least one side. and another supply hole provided in the sealing member for supplying pressurized fluid to another fluid film forming portion. 2. The fluid pressure cylinder according to claim 1, wherein the piston is provided with a seal portion at each end thereof.