JP2013185668A - Actuator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve operating stability of an output shaft, in an actuator having a constitution for supporting a piston by a hydrostatic bearings and using differential pressure acting to the piston to drive the output shaft.SOLUTION: An actuator includes a piston head 18 defining a constant pressure chamber 20 on one end side and an adjusted pressure chamber 22 at another end side between it and a cylinder 6, a driving means for driving the piston 8 by adjusting pressure between the constant pressure chamber 20 and the adjusting pressure chamber 22, a first hydrostatic bearing 70 formed by interposing compressed air between a one end side outer peripheral surface of the piston head 18 and an inner peripheral surface of the cylinder 6, and a second hydrostatic bearing 72 formed by interposing compressed air between the another end side outer peripheral surface of the piston head 18 and the inner peripheral surface of the cylinder 6, and a pressure supply means for supplying compressed air at constant pressure respectively to respective hydrostatic bearings even while differential pressure is produced between the constant pressure chamber 20 and the adjusted pressure chamber 22.

Description

  The present invention relates to an actuator, and more particularly to an actuator that drives an output shaft using differential pressure due to a working fluid.

  2. Description of the Related Art Conventionally, there is known an actuator that drives an output shaft by taking compressed air as a working fluid into a cylinder and applying an axial differential pressure to a piston. For example, Patent Document 1 discloses an actuator in which a constant pressure chamber is provided on one end side of a piston head in a cylinder and an adjustment pressure chamber is provided on the other end side, and the pressure in the adjustment pressure chamber is made variable to apply pressure to the piston. . Compressed air supplied from an external air pressure source is directly supplied to the constant pressure chamber while maintaining a constant pressure on the one hand, and is decompressed and adjusted via the servo valve on the other hand to the adjusted pressure chamber. By adjusting the pressure supplied to the adjustment pressure chamber by controlling the opening of the servo valve, the pressure difference between the adjustment pressure chamber and the constant pressure chamber, that is, the force acting on the piston can be adjusted.

  Pistons are supported by hydrostatic bearings that utilize their compressed air. That is, throttle grooves for introducing compressed air are formed at predetermined intervals in the circumferential direction on the outer peripheral surface on one end side and the outer peripheral surface on the other end side of the piston head, respectively, and a pair of hydrostatic bearing portions are configured. A first hydrostatic bearing is formed between the one hydrostatic bearing portion and the inner peripheral surface of the cylinder by introducing compressed air in a constant pressure chamber. A second hydrostatic bearing is formed between the other hydrostatic bearing portion and the inner peripheral surface of the cylinder by introducing the compressed air in the adjustment pressure chamber. With these hydrostatic bearings, the piston head can be lifted from the inner wall of the cylinder and slid in the axial direction in a non-contact state. At this time, the amount of movement of the piston, that is, the position of the output shaft can be controlled by adjusting the pressure acting on the piston head.

JP 2004-301138 A

  By the way, generally, when the pressure of the compressed air introduced into the hydrostatic bearing is increased, the amount of displacement of the piston head in the radial direction when an external force is applied is reduced. That is, the bearing rigidity is increased. Conversely, when the pressure of the compressed air introduced into the hydrostatic bearing is reduced, the amount of displacement of the piston head in the radial direction when an external force is applied increases. That is, the bearing rigidity is lowered. For this reason, when the pressure in the adjustment pressure chamber changes for output shaft position control and load control in the actuator as described above, the bearing rigidity of one of the hydrostatic bearings also changes. This can affect the operation of the output shaft. Such a problem can occur not only in compressed air but also in actuators using other compressible fluids.

  The present invention has been made in view of such a problem. In an actuator having a configuration in which a piston is supported by a hydrostatic bearing and driving an output shaft using a differential pressure acting on the piston, an output is provided. The purpose is to improve the operational stability of the shaft.

  In order to solve the above-described problems, an actuator according to an aspect of the present invention includes a cylinder into which a working fluid is introduced, a slidably accommodated in the cylinder, and a first pressure chamber on one end side and the other end between the cylinder A piston head that divides the second pressure chamber on the side, an output shaft that is coaxially connected to the piston head and extends to the outside of the cylinder, and a first pressure chamber and a second pressure chamber. Drive means for driving the piston by adjusting at least one pressure, and a first hydrostatic bearing formed by interposing a working fluid between the outer peripheral surface on one end side of the piston head and the inner peripheral surface of the cylinder A second hydrostatic bearing formed by interposing a working fluid between the outer peripheral surface of the other end side of the piston head and the inner peripheral surface of the cylinder, and between the first pressure chamber and the second pressure chamber Differential pressure is generated Also comprises a pressure supply means for supplying a working fluid pressure, respectively for each hydrostatic bearings in that state.

  According to this aspect, even in a state where a differential pressure is generated between the first pressure chamber and the second pressure chamber, that is, in a state where the differential pressure acts on both ends of the piston head, the first hydrostatic bearing and the second pressure bearing The fluid pressure applied to the hydrostatic bearing is maintained at a constant pressure. For this reason, the bearing rigidity of each hydrostatic bearing can be kept constant, and the operational stability of the output shaft can be improved.

  Another aspect of the present invention is also an actuator. The actuator includes a cylinder into which a working fluid is introduced, a piston head that is slidably accommodated in the cylinder, and divides a first pressure chamber on one end side and a second pressure chamber on the other end side between the cylinder and the cylinder. The piston is driven by adjusting the pressure of at least one of the first pressure chamber and the second pressure chamber, and a piston including an output shaft that is coaxially connected to the piston head and extends to the outside of the cylinder. A driving means, a first hydrostatic bearing formed by interposing a working fluid between an outer peripheral surface of one end of the piston head and an inner peripheral surface of the cylinder; an outer peripheral surface of the other end of the piston head; The second hydrostatic bearing formed by interposing a working fluid with the inner peripheral surface, and each hydrostatic bearing even in a state where a differential pressure is generated between the first pressure chamber and the second pressure chamber. Against the same pressure And a pressure supply means for supplying a working fluid.

  According to this aspect, even in a state where a differential pressure is generated between the first pressure chamber and the second pressure chamber, that is, in a state where the differential pressure acts on both ends of the piston head, the first hydrostatic bearing and the second pressure bearing The fluid pressure applied to the hydrostatic bearing is maintained at the same pressure. For this reason, the bearing rigidity of both hydrostatic bearings can be balanced, and the operational stability of the output shaft can be improved.

  According to the present invention, in an actuator having a configuration in which a piston is supported by a hydrostatic bearing and driving an output shaft using a differential pressure acting on the piston, the operational stability of the output shaft can be improved. it can.

It is a figure showing the schematic structure of the actuator which concerns on 1st Example. It is a figure showing the structure of a piston. It is explanatory drawing which shows the flow of compressed air when a static pressure bearing is functioning. It is a figure showing the structure of the piston which concerns on 2nd Example. It is explanatory drawing which shows the flow of compressed air when a static pressure bearing is functioning. It is a figure showing the structure of the piston which concerns on 3rd Example. It is explanatory drawing which shows the flow of compressed air when a static pressure bearing is functioning. It is explanatory drawing which shows the structure and operation | movement of an actuator which concern on 4th Example.

  An actuator according to an embodiment includes a cylinder into which a working fluid is introduced, a piston including a piston head that is slidably accommodated in the cylinder, and a driving unit that drives the piston. The working fluid may be compressed air, which will be described later, or other compressible fluid. A first pressure chamber is formed on one end side of the piston head in the cylinder, and a second pressure chamber is formed on the other end side. The output shaft of the actuator is coaxially connected to one side of the piston head, and its tip extends to the outside of the cylinder. The output shaft may transmit the driving force of the actuator to an external driving target, or may directly drive the external driving target. The drive means drives the piston in the axial direction by adjusting the pressure of at least one of the first pressure chamber and the second pressure chamber. Thereby, the output shaft operates in the axial direction. The drive means may individually adjust the fluid pressure introduced into each of the first pressure chamber and the second pressure chamber. Alternatively, the fluid pressure introduced into one pressure chamber may be reduced and supplied to the other pressure chamber.

  In such a configuration, the first hydrostatic bearing is formed by interposing a working fluid between the outer peripheral surface on one end side of the piston head and the inner peripheral surface of the cylinder. A second hydrostatic bearing is formed by interposing a working fluid between the outer peripheral surface of the other end side of the piston head and the inner peripheral surface of the cylinder. In particular, even when a differential pressure is generated between the first pressure chamber and the second pressure chamber, the pressure supply means supplies a constant pressure working fluid to each static pressure bearing. For this reason, the bearing rigidity of both the hydrostatic bearings can be kept constant, and as a result, the operational stability of the output shaft can be improved.

  A constant pressure is applied to each of the first hydrostatic bearing and the second hydrostatic bearing, but these pressures may be equal or different from each other. That is, even if the pressures are different from each other, if each pressure is constant, the bearing rigidity of each hydrostatic bearing can be made constant, and the operational stability of the output shaft can be improved. However, from the viewpoint of ensuring a balance of bearing rigidity, it is preferable to equalize the pressure applied to both hydrostatic bearings.

  In such a configuration, it is preferable that the working fluid is supplied to the second hydrostatic bearing from a pressure source having a pressure higher than that of the second pressure chamber. Thereby, the bearing rigidity of each hydrostatic bearing can be increased, and the supporting state can be further stabilized.

  Specifically, a control valve may be included as the driving means. A constant pressure chamber may be provided as the first pressure chamber, and an adjustment pressure chamber may be provided as the second pressure chamber. The working fluid supplied from the outside is supplied to the constant pressure chamber as it is to maintain the constant pressure, and on the other hand, the pressure is adjusted through a control valve and supplied to the adjusted pressure chamber. The force acting on the piston head can be adjusted by changing the set pressure of the control valve. The control valve may be driven to open and close by a mechanism using a solenoid or permanent magnet, or may be driven to open and close by a motor.

  More specifically, fluid passages are provided for supplying the working fluid of the constant pressure source to each of the first hydrostatic bearing and the second hydrostatic bearing. For example, it is preferable to provide a fluid passage for supplying a constant pressure working fluid introduced into the constant pressure chamber to each of the first hydrostatic bearing and the second hydrostatic bearing. Thus, by using the fluid pressure in the constant pressure chamber as it is, it is possible to simplify the configuration for supplying constant pressure to each static pressure bearing by the actuator. That is, it is not necessary to separately provide an additional pressure source or individual fluid passage, and the entire actuator can be simply configured. Moreover, since the working fluid supplied from the outside can be supplied to each hydrostatic bearing without reducing the pressure, the bearing rigidity of both hydrostatic bearings can be maintained high. As a result, the supporting state of the piston head, and thus the operating state of the output shaft can be maintained stably.

  In such a configuration, it is preferable to restrict the flow of the working fluid introduced into the second hydrostatic bearing into the adjustment pressure chamber so as not to affect the setting of the adjustment pressure in the adjustment pressure chamber. In addition, it is preferable to restrict the inflow of the working fluid from the adjustment pressure chamber to the second hydrostatic bearing so as not to affect the bearing rigidity of the second hydrostatic bearing. Therefore, a seal portion for restricting the flow of the working fluid between the second hydrostatic bearing and the second pressure chamber may be provided on the outer periphery of the piston.

  Thereby, it is possible to prevent or suppress a relatively high pressure working fluid in the hydrostatic bearing from flowing into the adjustment pressure chamber, and it is possible to stably maintain the differential pressure adjustment by the control valve. Further, the bearing rigidity of the second hydrostatic bearing can be stably maintained. As the seal portion, for example, a flexible seal member such as an O-ring may be fitted on the outer peripheral surface of the piston, but a partition protruding on the outer periphery may be integrally formed when the piston is molded. Or you may form the labyrinth seal by uneven | corrugated shape in the outer peripheral surface of a piston, and may control the flow of a working fluid. In order to take advantage of the hydrostatic bearing that reduces the operating resistance, it is preferable that the seal portion does not slide on the inner peripheral surface of the cylinder.

  The piston may be provided with a bypass passage that allows the first hydrostatic bearing and the second hydrostatic bearing to communicate with each other. That is, an introduction port communicating with the first hydrostatic bearing, an outlet port communicating with the second hydrostatic bearing, and a communication path connecting the inlet port and the outlet port may be formed in the piston. With such a configuration, the constant pressure supplied to the first hydrostatic bearing can be supplied to the second hydrostatic bearing through the inside of the piston.

  The piston may be formed with a discharge passage for introducing the working fluid from each of the first hydrostatic bearing and the second hydrostatic bearing and discharging the fluid from the output shaft to the outside. That is, a first outlet port that communicates with the first hydrostatic bearing, a second outlet port that communicates with the second hydrostatic bearing, a discharge port that communicates with the outside of the cylinder in the output shaft, and their outlet ports The piston may be formed with a communication path connecting the outlet and the discharge port. In addition, by providing the discharge passage in the piston, it is possible to prevent the discharged working fluid from affecting the pressure of the constant pressure chamber, the adjustment pressure chamber, and each of the hydrostatic bearings with a simple configuration.

  In an actuator according to another embodiment, even in a state where a differential pressure is generated between the first pressure chamber and the second pressure chamber, the pressure supply means is connected to the first hydrostatic bearing and the second hydrostatic bearing. On the other hand, a working fluid of the same pressure is supplied. According to such a configuration, since both the hydrostatic bearings balance at the same pressure, the operational stability of the output shaft can be improved. In addition, although the pressure of both hydrostatic bearings may fluctuate, in order to improve stability more, it is preferable that it is a constant pressure.

  DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments embodying the present invention will be described below in detail with reference to the drawings. In the following embodiments, the actuator of the present invention is embodied as a fluid pressure actuator (air actuator) using compressed air as a working fluid.

[First embodiment]
FIG. 1 is a diagram illustrating a schematic configuration of the actuator according to the first embodiment. The actuator 1 is configured by assembling an actuator body 2 and a servo valve 4. The actuator body 2 includes a cylinder 6 into which compressed air is introduced, a piston 8 that is slidably supported in the cylinder 6, pressure sensors 10 and 12 that detect pressure in the cylinder 6, and a position that detects the position of the piston 8. A sensor 14 is provided.

  The actuator 1 is connected to a pressure source 16 such as an air tank installed outside. The compressed air delivered from the pressure source 16 maintains a substantially constant pressure, and is directly introduced into the first pressure chamber in the cylinder 6 on the one hand, and on the other hand to the second pressure chamber in the cylinder 6 via the servo valve 4. be introduced. The servo valve 4 applies a force in the axial direction to the piston 8 by reducing the pressure of the introduced compressed air and supplying it to the cylinder 6. This force becomes the driving force of the piston 8. The servo valve 4 is driven by a driver 100.

  The cylinder 6 has a circular hole-shaped pressure space that passes through the prismatic main body along the central axis, and accommodates the piston 8 in the pressure space. The piston 8 partitions the pressure space of the cylinder 6 in the axial direction by the piston head 18. That is, a constant pressure chamber 20 (first pressure chamber) is formed on one end side of the piston head 18 in the cylinder 6, and an adjustment pressure chamber 22 (second pressure chamber) is formed on the other end side. The pressure sensor 10 detects the pressure in the constant pressure chamber 20, and the pressure sensor 12 detects the pressure in the adjustment pressure chamber 22. The detection signal of each pressure sensor is input to the driver 100.

  An inlet port 24 that communicates with the pressure source 16, a lead-out port 26 that communicates with the inlet of the servo valve 4, and an introduction port 28 that communicates with the outlet of the servo valve 4 are provided on the side of the cylinder 6. The inlet port 24 communicates with the constant pressure chamber 20 on the one hand, and communicates with the outlet port 26 via the communication passage 30 on the other hand. The introduction port 28 communicates with the adjustment pressure chamber 22 via the communication path 32.

  With such a configuration, the compressed air supplied from the pressure source 16 is directly introduced into the constant pressure chamber 20 on the one hand, and reduced in pressure via the servo valve 4 on the other hand, and introduced into the regulated pressure chamber 22. Thereby, the driving force by the pressure is applied to the piston head 18.

  An output shaft 34 is coaxially connected to one end of the piston head 18. The front end of the output shaft 34 passes through one end of the cylinder 6 and extends to the outside, and transmits the driving force in the axial direction to a driving target (not shown). On the other hand, on the other end side of the piston head 18, a small-diameter sensor rod 36 is connected coaxially. A position sensor 14 is fixed to the other end side of the cylinder 6. The position sensor 14 is inserted through the sensor rod 36 and outputs a detection signal for detecting the amount of displacement in the axial direction.

  Specifically, a magnetic body and a non-magnetic body are alternately arranged in the axial direction of the sensor rod 36, and the position sensor 14 detects the magnetic body as the sensor rod 36 is displaced. A detection signal from the position sensor 14 is input to the driver 100. The driver 100 can determine the position of the piston 8 (that is, the position of the output shaft 34) based on the number of times detected by the position sensor 14. Since the configuration and operation of such a position sensor are known as described in, for example, Patent Document 1 described above, detailed description thereof is omitted.

  The servo valve 4 is configured as an electromagnetic valve capable of controlling the differential pressure across the front and back to a magnitude corresponding to the value of an externally supplied current. The servo valve 4 depressurizes and adjusts the pressure of the compressed air introduced through the communication passage 30 and supplies the adjusted pressure to the adjustment pressure chamber 22 through the communication passage 32. Since the configuration and operation of such a servo valve are known as described in, for example, Patent Document 1 described above, detailed description thereof is omitted.

  The driver 100 supplies a control current corresponding to a position command and a load command input from an external controller (not shown) to the servo valve 4 to adjust the pressure (adjusted pressure) in the adjusted pressure chamber 22. The driver 100 acquires the position of the output shaft 34 based on the detection value of the position sensor 14, and calculates the differential pressure (driving force) acting on the piston 8 based on the detection values of the pressure sensors 12 and 14. Then, the pressure of the adjustment pressure chamber 22 is controlled so that the position of the output shaft 34 becomes a position according to the position command, or the driving force (load) transmitted by the output shaft 34 becomes a value according to the load command.

Next, the structure of the piston 8 and its surroundings, which are the main parts of this embodiment, will be described.
FIG. 2 is a diagram illustrating the configuration of the piston 8. 2A is a plan view of the piston 8, and FIG. 2B is a cross-sectional view taken along the line AA in FIG. 2A. FIG. 3 is an explanatory diagram showing the flow of compressed air when the hydrostatic bearing is functioning. FIG. 3 shows a cross section different from FIG. 1, and the notation of the servo valve 4 etc. is omitted for convenience. The arrows in the figure indicate the flow of compressed air.

  As shown in FIG. 2A, the piston 8 has a stepped columnar piston head 18. The piston head 18 is configured such that both ends are larger in diameter than the central portion, a bearing portion 40 for forming a first hydrostatic bearing is provided at one end, and a second static pressure bearing is provided at the other end. A bearing portion 42 for forming a pressure bearing is provided. At a plurality of locations on the outer peripheral surface of the piston head 18, annular projections for restricting the flow of compressed air are provided. That is, convex portions 44 and 46 are provided between the bearing portion 40 and the bearing portion 42 so as to be adjacent to the respective bearing portions. A convex portion 48 is also provided on the opposite side of the bearing portion 42 from the convex portion 46. The plurality of convex portions are integrally formed in the process of forming the piston 8. In the present embodiment, the bearing portions 40, 42 and the convex portions 44, 46, 48 have substantially the same outer diameter.

  The bearing portion 40 is provided with a plurality of rectangular bearing grooves 50 at regular intervals in the circumferential direction. Each bearing groove 50 is opened only to one end side of the piston head 18 (that is, the side opposite to the convex portion 44). On the other hand, the bearing portion 42 is also provided with a plurality of rectangular bearing grooves 52 at regular intervals in the circumferential direction. Each bearing groove 52 is opened only on the center side of the piston head 18 (that is, on the convex portion 46 side).

  On the other hand, as shown in FIG. 2B, the piston 8 is provided with an introduction port 54 in the vicinity of one end side of the bearing portion 40, and an outlet port 56 is provided between the bearing portion 42 and the convex portion 46. Yes. A bypass passage 58 that connects the inlet 54 and the outlet 56 is formed. Further, the piston 8 is provided with a lead-out port 60 between the bearing portion 40 and the convex portion 44, a lead-out port 62 is provided between the bearing portion 42 and the convex portion 48, and further at the tip of the inlet port 24. A discharge port 64 is provided. A discharge passage 66 that connects the outlet 60 and the outlet 64 and connects the outlet 62 and the outlet 64 is formed.

  With the above configuration, as shown in FIG. 3, the outer peripheral surface of the bearing portions 40, 42 and the convex portions 44, 46, 48 and the inner peripheral surface of the cylinder 6 when the piston 8 is assembled to the cylinder 6. A narrowed portion due to a minute clearance is formed between the two. That is, a so-called labyrinth seal is formed by the concavo-convex shape in the axial direction formed by the bearing portion and the convex portion, and the flow of compressed air through the gap between the piston head 18 and the cylinder 6 is restricted.

  On the other hand, each bearing groove 50 of the bearing portion 40 is opened only to the constant pressure chamber 20 side, and the compressed air in the constant pressure chamber 20 is introduced. Further, each bearing groove 52 of the bearing portion 42 is opened only to a pressure space between the bearing portion 42 and the convex portion 46, and compressed air in the pressure space is introduced. That is, the constant pressure compressed air in the constant pressure chamber 20 is introduced into each bearing groove 50 of the bearing portion 40 and is also introduced into the bearing groove 52 of the bearing portion 42 via the bypass passage 58 (see solid arrows). ).

  Thereby, the first hydrostatic bearing 70 is formed between the outer peripheral surface of the bearing portion 40 and the inner peripheral surface of the cylinder 6, and the second hydrostatic bearing 70 is formed between the outer peripheral surface of the bearing portion 42 and the inner peripheral surface of the cylinder 6. The hydrostatic bearing 72 is formed (see the one-dot chain line portion). Since the compressed air in the constant pressure chamber 20 is also discharged from the clearance between the one end of the cylinder 6 and the output shaft 34, a static pressure bearing is formed between the two. That is, in the actuator 1, the constant pressure compressed air in the constant pressure chamber 20 is discharged along the outer surface of the output shaft 34 to the tip side, and the constant pressure compressed air is discharged to the bearing portions 40, 42 of the piston head 18. The hydrostatic bearing is formed by flowing into the nozzle. By lifting the piston head 18 from the inner wall of the cylinder 6 by these hydrostatic bearings, the piston 8 can be slid in the cylinder 6 without contact.

  At this time, a part of the compressed air forming the static pressure bearing 70 is discharged through the discharge passage 66 between the bearing portion 40 and the convex portion 44. A part of the compressed air forming the hydrostatic bearing 72 is discharged through the discharge passage 66 between the bearing portion 42 and the convex portion 48 (see the dotted arrow). Further, since the labyrinth seal described above functions, the relatively high pressure compressed air in the constant pressure chamber 20 is restricted from flowing into the adjustment pressure chamber 22. That is, high pressure compressed air is prevented from flowing into the adjustment pressure chamber 22 and affecting the setting of the adjustment pressure.

  As described above, in the actuator 1 of the present embodiment, in a state where a differential pressure is generated between the constant pressure chamber 20 and the adjustment pressure chamber 22, that is, in a state where the differential pressure acts on both ends of the piston head 18. Also, the fluid pressure applied to the first hydrostatic bearing 70 and the second hydrostatic bearing 72 is supplied from the constant pressure chamber 20 and held at a constant pressure. For this reason, the bearing rigidity of both the hydrostatic bearings can be kept constant at the same pressure. As a result, the operational stability of the output shaft 34 can be improved.

[Second Embodiment]
The actuator according to the present embodiment is substantially the same as that of the first embodiment except that the configuration of the piston is different. For this reason, the same components as those in the first embodiment are denoted by the same reference numerals and the description thereof is omitted. FIG. 4 is a diagram illustrating the configuration of the piston according to the second embodiment. 4A is a plan view of the piston, and FIG. 4B is a cross-sectional view taken along the line AA in FIG. 4A. FIG. 5 is an explanatory diagram showing the flow of compressed air when the hydrostatic bearing is functioning.

  As shown in FIG. 4A, in the piston 208 of this embodiment, each bearing groove 52 is opened to the convex portion 48 side in the bearing portion 242 on the other end side of the piston head 218. 4B, the outlet 56 of the bypass passage 258 is provided between the bearing portion 242 and the convex portion 48. On the other hand, the outlet 62 of the discharge passage 266 is provided between the bearing portion 242 and the convex portion 46. That is, the arrangement of the bearing grooves 52 in the bearing portion 242 is opposite to that in the first embodiment.

  Even in such a configuration, as shown in FIG. 5, when the piston 208 is assembled to the cylinder 6, a seal is formed by the bearing portion and the convex portion, and the gap between the piston head 218 and the cylinder 6 is interposed. Therefore, the distribution of compressed air is restricted. Further, the constant pressure compressed air in the constant pressure chamber 20 is introduced into each bearing groove 50 of the bearing portion 40, and is also introduced into the bearing groove 52 of the bearing portion 242 through the bypass passage 258.

  Thus, a first hydrostatic bearing 70 is formed between the outer peripheral surface of the bearing portion 40 and the inner peripheral surface of the cylinder 6, and the second hydrostatic bearing 70 is formed between the outer peripheral surface of the bearing portion 242 and the inner peripheral surface of the cylinder 6. The hydrostatic bearing 272 is formed. And it becomes possible to keep the bearing rigidity of both hydrostatic bearings constant at the same pressure. As a result, the operational stability of the output shaft 34 can be improved. However, since the number of irregularities between the second hydrostatic bearing 272 and the adjustment pressure chamber 22 is smaller than that in the first embodiment, the configuration of the first embodiment is preferable from the viewpoint of further improving the sealing performance. It can be said.

[Third embodiment]
The actuator according to the present embodiment is substantially the same as the first and second embodiments except that the configuration of the piston is different. For this reason, the same components as those in the first and second embodiments are denoted by the same reference numerals and the description thereof is omitted. FIG. 6 is a diagram illustrating the configuration of the piston according to the third embodiment. 6A is a plan view of the piston, and FIG. 6B is a cross-sectional view taken along the line AA in FIG. 6A. FIG. 7 is an explanatory diagram showing the flow of compressed air when the hydrostatic bearing is functioning.

  As shown in FIG. 6A, in the piston 308 of this embodiment, each bearing groove 50 is opened to the center side of the piston head 318 in the bearing portion 340 on one end side of the piston head 318. Further, the inner convex portions 44 and 46 as in the first embodiment are not provided. On the other hand, a convex portion 344 is provided on the outer side (one end side) of the bearing portion 340, and a lead-out port 60 is provided between the bearing portion 340 and the convex portion 344. As shown in FIG. 6B, the outlet 56 of the bypass passage 358 is provided at the center of the piston head 318. On the other hand, an outlet 62 is provided between the bearing portion 42 and the convex portion 48. The outlets 60 and 62 are connected to the outlet 64 through the outlet passage 366.

  With such a configuration, as shown in FIG. 7, the constant pressure compressed air in the constant pressure chamber 20 is guided to the pressure space in the center of the piston head 318 via the bypass passage 358, and each bearing groove of the bearing portion 340. 50 and each bearing groove 52 of the bearing portion 42. Thereby, a first hydrostatic bearing 370 is formed between the outer peripheral surface of the bearing portion 340 and the inner peripheral surface of the cylinder 6, and the second hydrostatic bearing 370 is formed between the outer peripheral surface of the bearing portion 42 and the inner peripheral surface of the cylinder 6. The hydrostatic bearing 72 is formed. And it becomes possible to keep the bearing rigidity of both hydrostatic bearings constant at the same pressure. As a result, the operational stability of the output shaft 34 can be improved.

  Such a configuration is effective when there is no mechanical restriction such as no other pressure entering or leaving the central pressure space of the piston head 318. In other words, for example, in a configuration in which the actuator is mounted on a chip mounter and the like, and outside air is sucked from the tip of the output shaft 34, a suction passage that connects the center of the piston head 318 and the tip of the output shaft 34 is formed. There is something to do. For such an actuator, it is preferable to adopt the configurations of the first and second embodiments.

[Fourth embodiment]
The actuator according to the present embodiment is different from the first to third embodiments in that it has a plurality of constant pressure sources and supplies a pair of static pressure bearings with constant pressure compressed air from the second pressure source. Hereinafter, the same components as those in the first to third embodiments are denoted by the same reference numerals and the description thereof is omitted. FIG. 8 is an explanatory diagram showing the configuration and operation of the actuator according to the fourth embodiment.

  In the actuator of the present embodiment, as in the third embodiment, each bearing groove 50 of the bearing portion 340 and each bearing groove 52 of the bearing portion 42 are both open to the pressure space 419 in the center of the piston head 418. On the other hand, the piston 408 is not provided with a bypass passage that allows the central pressure space 419 and the constant pressure chamber 20 to communicate with each other. Constant pressure compressed air is supplied from the second pressure source 416 through a supply passage 420 provided in the center of the cylinder 406.

  In the present embodiment, the pressure of the compressed air supplied from the second pressure source 416 to the central pressure space 419 is higher than the pressure of the compressed air supplied from the first pressure source 16 to the constant pressure chamber 20. However, it may be the same pressure or a low pressure. In the case of the same pressure, the second pressure source 416 may be omitted, and a part of the compressed air supplied from the first pressure source 16 may be supplied also to the pressure space 419. Even in such a configuration, the bearing rigidity of both the hydrostatic bearings can be kept constant at the same pressure. As a result, the operational stability of the output shaft 34 can be improved.

  In the above, this invention was demonstrated based on the Example. This embodiment is merely an example, and it will be understood by those skilled in the art that various modifications can be made to the combination of each component and each processing process, and such modifications are within the scope of the present invention. is there.

  In the above-described embodiment, the example in which the constant pressure chamber is provided on the output shaft side of the piston head in the cylinder and the adjustment pressure chamber is provided on the side opposite to the output shaft is shown. In a modification, an adjustment pressure chamber may be provided on the output shaft side of the piston head in the cylinder, and a constant pressure chamber may be provided on the opposite side of the output shaft. Even in such a configuration, a constant pressure working fluid is supplied to the first hydrostatic bearing and the second hydrostatic bearing. Preferably, the working fluid in the constant pressure chamber is supplied to both hydrostatic bearings.

  In the said Example, the air actuator which uses compressed air as a working fluid was illustrated. In a modification, the same configuration may be applied to a fluid pressure actuator that uses other compressive fluids such as compressible gas, oil, and water as the working fluid.

  In the said Example, the structure which forms a pair (two) hydrostatic bearing in a piston head was illustrated. In a modified example, three or more hydrostatic bearings may be formed on the piston head. Even in such a configuration, a constant pressure (preferably the same pressure) working fluid is supplied to each hydrostatic bearing.

  DESCRIPTION OF SYMBOLS 1 Actuator, 2 Actuator main body, 4 Servo valve, 6 Cylinder, 8 Piston, 16 Pressure source, 18 Piston head, 20 Constant pressure chamber, 22 Adjustment pressure chamber, 30, 32 Communication path, 34 Output shaft, 40, 42 Bearing part 44, 46, 48 Convex, 50, 52 Bearing groove, 58 Bypass passage, 66 Discharge passage, 70, 72 Hydrostatic bearing, 208 Piston, 218 Piston head, 242 Bearing portion, 258 Bypass passage, 266 Discharge passage, 272 Hydrostatic bearing, 308 Piston, 318 Piston head, 340 Bearing part, 358 Bypass passage, 366 Discharge passage, 370 Static pressure bearing, 406 Cylinder, 408 Piston, 416 Pressure source, 418 Piston head, 419 Pressure space, 420 Supply passage.

Claims (9)

A cylinder into which the working fluid is introduced;
A piston head that is slidably accommodated in the cylinder and divides the first pressure chamber on one end side and the second pressure chamber on the other end side between the cylinder and the piston head, and is coaxially connected to the piston head. A piston including an output shaft extending to the outside of the cylinder,
Drive means for driving the piston by adjusting the pressure of at least one of the first pressure chamber and the second pressure chamber;
A first hydrostatic bearing formed by interposing a working fluid between an outer peripheral surface at one end of the piston head and an inner peripheral surface of the cylinder;
A second hydrostatic bearing formed by interposing a working fluid between the outer peripheral surface of the other end side of the piston head and the inner peripheral surface of the cylinder;
Pressure supply means for supplying a constant-pressure working fluid to each hydrostatic bearing even in a state where a differential pressure is generated between the first pressure chamber and the second pressure chamber;
An actuator comprising:   2. The actuator according to claim 1, wherein a working fluid is supplied to the second hydrostatic bearing from a pressure source having a pressure higher than that of the second pressure chamber. As the first pressure chamber, a constant pressure chamber into which a constant pressure working fluid is introduced from the outside,
A control valve for introducing a part of the constant-pressure working fluid to reduce the pressure, and for deriving the working fluid controlled to the adjustment pressure for adjusting the differential pressure;
As the second pressure chamber, an adjustment pressure chamber into which a working fluid having passed through the control valve is introduced,
The actuator according to claim 1, further comprising:   The fluid passage for supplying the working fluid of the pressure source of constant pressure to each of said 1st hydrostatic bearing and said 2nd hydrostatic bearing is provided, The any one of Claims 1-3 characterized by the above-mentioned. The actuator according to Crab.   5. The actuator according to claim 4, wherein the fluid passage connects a constant pressure chamber as a pressure source of the constant pressure and each of the first hydrostatic bearing and the second hydrostatic bearing. .   A working fluid having an adjusted pressure is introduced into the second pressure chamber, and a seal portion for restricting the flow of the working fluid between the second static pressure bearing and the second pressure chamber is provided. The actuator according to claim 4 or 5, characterized by the above.   The actuator according to claim 1, wherein a bypass passage is formed in the piston to communicate the first hydrostatic bearing and the second hydrostatic bearing.   A discharge passage is formed in the piston for introducing a working fluid from each of the first hydrostatic bearing and the second hydrostatic bearing and discharging the fluid from the output shaft to the outside. The actuator according to claim 1. A cylinder into which the working fluid is introduced;
A piston head that is slidably accommodated in the cylinder and divides the first pressure chamber on one end side and the second pressure chamber on the other end side between the cylinder and the piston head, and is coaxially connected to the piston head. A piston including an output shaft extending to the outside of the cylinder,
Drive means for driving the piston by adjusting the pressure of at least one of the first pressure chamber and the second pressure chamber;
A first hydrostatic bearing formed by interposing a working fluid between an outer peripheral surface at one end of the piston head and an inner peripheral surface of the cylinder;
A second hydrostatic bearing formed by interposing a working fluid between the outer peripheral surface of the other end side of the piston head and the inner peripheral surface of the cylinder;
Pressure supply means for supplying a working fluid of the same pressure to each hydrostatic bearing even in a state where a differential pressure is generated between the first pressure chamber and the second pressure chamber;
An actuator comprising:

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