JP4530868B2 - Static pressure gas bearing and gas pressure actuator for piston drive mechanism - Google Patents

Description

The present invention relates to a static pressure gas bearing and a gas pressure actuator of a piston drive mechanism including a piston and a cylinder, and more particularly to a static pressure gas bearing that floats and supports a straight shaft of a piston drive mechanism with respect to a housing by the gas pressure. The present invention relates to a gas pressure actuator including a gas bearing .

  As is well known, a piston drive mechanism including a piston and a cylinder is used in various industrial fields as an actuator using fluid pressure. As the fluid pressure for driving the piston, in addition to hydraulic pressure and vapor pressure, gas pressure such as dry air or inert gas is used. In particular, a gas pressure piston drive mechanism using gas pressure is expected to be an easy-to-handle drive mechanism with less contamination problems than those using hydraulic pressure. For example, a pneumatic servo cylinder is used to suppress vehicle shaking. It is described in Patent Document 1. In this piston drive mechanism, the rectilinear shaft for taking out the driving force to the outside is supported by a bearing with the housing constituting the cylinder. This support bearing structure is for sliding support in the straight direction, but is devised so that fluid pressure is not released by movement in the axial direction. For example, a surface support structure that is precisely finished is used.

Japanese Patent Laid-Open No. 10-129478

  In addition to preventing the vehicle from shaking, a piston drive mechanism using gas pressure has been studied. For example, in a testing machine such as a tension / compression testing machine, it is necessary to accurately control displacement and load, and a piston driving mechanism using gas pressure is expected from the convenience of handling.

  In this case, it is conceivable to adopt a gas bearing structure for the bearing between the linear shaft and the housing. If gas pressure is used for both piston drive and bearing support, contamination will be eliminated and the movement will be smoother. For example, it is expected to improve accuracy in testing machines such as tensile and compression testing machines.

  In the gas bearing structure, gas pressure is supplied to a gap between the linear shaft and the housing, and the linear shaft is floated with respect to the housing by the static pressure. Therefore, when a radial impact of the shaft exceeding the levitation pressure is applied between the rectilinear shaft and the housing, the rectilinear shaft collides with the housing, and the sliding surface of the bearing structure is damaged or deformed to cause a test or the like. Therefore, it may be difficult to perform the operation.

An object of the present invention is to provide a static pressure gas bearing of a piston drive mechanism and a gas pressure actuator including the static pressure gas bearing, which can prevent damage to a bearing sliding surface against a radial impact in the piston drive mechanism. It is.

The static pressure gas bearing of the piston drive mechanism according to the present invention is a static pressure gas bearing that floats and supports the linear shaft of the piston drive mechanism relative to the housing, and an impact provided on the gas receiving surface of the linear drive shaft and the gas receiving wall of the housing. A micro-indentation provided on at least one of a solid or liquid lubricating layer for buffering and a gas receiving surface or a gas receiving wall and having a depth shallower than the thickness of the lubricating layer and a surface diameter smaller than the thickness of the lubricating layer A plurality of lubricant reservoirs .

Further, in the static pressure gas bearing of the piston drive mechanism according to the present invention , the gas supplied from the gas supply path is a shallow groove provided along the axial direction on the inner surface of the housing that supports the linear shaft of the piston drive mechanism. And a shallow groove surface restriction that floats and supports the rectilinear shaft relative to the housing. It is preferable to be provided .

Moreover, it is preferable that the lubricating layer includes grease. Further, the lubricating layer is preferably configured to include molybdenum disulfide by WPC treatment.
A gas pressure actuator according to the present invention includes the static pressure gas bearing of the piston drive mechanism.

  According to the above configuration, since the solid or liquid lubricating layer for the shock buffer is provided on the gas receiving surface of the straight shaft and the gas receiving wall of the housing, the bearing sliding surface is damaged due to the radial shock in the piston drive mechanism. Can be prevented. Normally, the gas bearing is made of a clean gas and a clean surface in order to supply a precisely controlled gas pressure to the minute gap. Unlike the general common sense, the above-described configuration is based on the fact that a lubricating layer is provided, that is, a so-called controlled dirty surface, has been confirmed to sufficiently exhibit the function of the gas bearing.

  In addition, since the gas receiving surface or the gas receiving wall has a plurality of lubricant reservoirs of minute recesses, the lubricant is held in the minute recesses, and the function of the buffer during impact can be exhibited for a long period of time.

Moreover, since the lubricating layer contains grease and molybdenum disulfide by WPC treatment, a lubricant having a known lubricating property can be used.
The gas pressure actuator includes a static pressure gas bearing of the piston drive mechanism having the above-described configuration. Here, since the static pressure gas bearing of the piston drive mechanism is provided with a solid or liquid lubricating layer for a buffer at the time of impact on the gas receiving surface of the rectilinear shaft and the gas receiving wall of the housing, the radial shock in the piston drive mechanism It is possible to prevent the bearing sliding surface from being damaged.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Hereinafter, the static pressure gas bearing of the piston drive mechanism used in the tensile compression tester will be described. However, the object to which the static pressure gas bearing of the piston drive mechanism is applied is not limited to such a tester. Any device that floats and supports the rectilinear shaft relative to the housing can be applied. For example, it may be a general actuator that supports a straight shaft with a static pressure gas bearing. In addition, the numerical values such as the dimensions of the shaft and the thickness of the lubricating layer used in the following description are examples, and any combination of other numerical values can be used as long as the floating support that is a function of the static pressure gas bearing can be sufficiently secured. There may be.

  FIG. 1 is a diagram showing a configuration of a piston drive mechanism 10 for a tension / compression test machine in which a static pressure gas bearing 100 is used. The piston drive mechanism 10 includes a piston rod 12, a housing 20 having a cylinder function, and a gas pressure control valve 40 that supplies a controlled gas pressure. The static pressure gas bearing 100 is provided where the piston rod 12 is supported so as to be movable in the axial direction with respect to the housing 20. Further, a manifold 30 is provided between the gas pressure control valve 40 and the housing 20, and the gas pressure controlled by the gas pressure control valve 40 is guided to the inside of the housing 20 by the control gas flow paths 32 and 34. The one end of the piston rod 12 is connected to an object of a tensile / compression test via a load cell 16 that detects a load, and the displacement sensor 50 detects the axial displacement of the piston rod 12 at the other end. Is provided.

In the piston drive mechanism 10, the piston rod 12 has a flange portion 14, the interior of the housing 20 is divided into front and rear gas chambers 36 and 38, and gas controlled by a gas pressure control valve 40 in each gas chamber 36 and 38. Pressure is supplied through the control gas flow paths 32 and 34, and the flange portion 14 is driven to move in the axial direction, that is, in the X direction shown in FIG. 1, due to the difference in gas pressure between the front and rear gas chambers 36 and 38. Thus, the piston drive mechanism 10 used in the tension and compression testing machine, the piston rod 12 is axially moved by the gas pressure, not shown, via a load cell 16 provided at the tip end of a piston rod 12 It has a function of applying a load to the test object and measuring the displacement at that time.

  The piston rod 12 is an elongated rod-like member having a function of a load shaft in a tensile / compression tester, and has a flange portion 14 having a large diameter at a substantially intermediate portion in the axial direction. Since the outer periphery of the flange portion 14 may slide or come into contact with the inner peripheral wall of the housing 20, it is preferable that a sufficiently smooth surface treatment and an appropriate curing treatment be performed as necessary. Further, both ends of the piston rod 12 are supported on the housing 20 so as to be axially freely movable, but it is preferable that the portions are similarly subjected to a sufficiently smooth surface treatment and an appropriate curing treatment as necessary. Such a piston rod 12 can be obtained by processing a metal material having sufficient mechanical rigidity and performing a necessary surface treatment or the like. For example, a material such as high-tensile duralumin, high-strength stainless steel or tool steel can be processed into a cylinder with a flange and subjected to surface hardening treatment, surface polishing treatment, lubrication plating treatment, or the like.

  As described above, the load cell 16 for detecting the load is attached to the one end of the piston rod 12. As the load cell 16, for example, a load table provided with a strain gauge or the like can be used. Further, as described above, the displacement sensor 50 is provided at the other end of the piston rod 12. The displacement sensor 50 may be a differential transformer type. That is, a part of the other end of the piston rod 12 is extended to attach the soft magnetic probe 52, and a transformer winding 54 is provided on the housing 20 side in cooperation therewith. The soft magnetic probe 52 moves in the axial direction integrally with the piston rod 12, and a signal corresponding to the insertion length of the transformer winding 54 into the cavity is output from the transformer winding 54. The axial displacement of the piston rod 12 can be detected. As the displacement sensor 50, a commonly used type such as an optical type or a magnetic type may be used.

  The outputs of the load cell 16 and the displacement sensor 50 are used as they are as load-displacement data of a tension / compression tester, and fed back to a control unit of a tension / compression tester (not shown) to be used as control data for the gas pressure control valve 40. It is done.

  The housing 20 is a one-time airtight housing that has a function of accommodating the flange portion 14 of the piston rod 12 inside, projecting both ends of the piston rod 12 to the outside, and guiding and supporting the piston rod 12 freely in the axial direction. Here, the term “airtight” means that the piston rod 12 is sufficiently airtight in terms of the performance of the tensile / compression tester, except when the piston rod 12 is abnormally inclined in the axial direction due to a radial impact or the like. The housing 20 includes a cylinder tube 22 and front and rear end plates 24 and 26. That is, the front and rear end plates 24 and 26 constituting the static pressure gas bearing 100 are respectively disposed between both ends of the piston rod 12 at both side openings of the substantially annular cylinder tube 22 to constitute a cylinder housing as a whole. To do.

  The cylinder tube 22 is an annular member having an inner diameter slightly larger than the diameter of the flange portion 14 of the piston rod 12. Since the inner peripheral wall may slide or come into contact with the outer periphery of the flange portion 14 of the piston rod 12, it is preferable that the inner peripheral wall be subjected to a sufficiently smooth surface treatment and an appropriate curing treatment as necessary. Such a cylinder tube 22 can be obtained by processing a metal material having sufficient mechanical rigidity and performing a necessary surface treatment or the like. For example, the outer and inner circumferences of appropriate pipe materials made of materials such as high-tensile duralumin, high-strength stainless steel, and tool steel are processed into predetermined dimensions and used after being subjected to surface hardening treatment, surface polishing treatment, lubrication plating treatment, etc. it can.

  The front and rear end plates 24 and 26 are a pair of members having substantially the same shape. The front and rear end plates 24 and 26 have a rod support hole that supports the piston rod 12 through the center, and the piston rod 12 blocks the openings on both sides of the cylinder tube 22. It is a member having a function of supporting the rod 12 so as to be movable in the axial direction. The inner diameter of the rod support hole is slightly larger than the diameters at both ends of the piston rod 12. The rod support hole is provided with an exhaust groove 42, a shallow groove surface constriction 46, and the like, and constitutes the static pressure gas bearing 100 together with the piston rod 12. Details thereof will be described later. The front and rear end plates 24, 26 have control gas flow paths 32, 34 that guide the controlled gas pressure from the gas pressure control valve 40 to the inside of the housing 20 through the manifold 30. In addition, a stopper 56 is provided to reduce the impact when the axial movement of the piston rod 12 is too large and the flange portion 14 collides with the front and rear end plates 24 and 26. Such front and rear end plates 24 and 26 can be obtained by processing a metal material having sufficient mechanical rigidity and performing a necessary surface treatment or the like. For example, a material such as high-tensile duralumin, high-strength stainless steel or tool steel can be processed into a cylinder with a flange and subjected to surface hardening treatment, surface polishing treatment, lubrication plating treatment, or the like.

  The cylinder tube 22, the front and rear end plates 24 and 26, and the piston rod 12 are assembled in the following procedure. That is, first, the piston rod 12 is passed through the cylinder tube 22. Next, the front end plate 24 is disposed on the load cell 16 side, the rear end plate 26 is disposed on the displacement sensor 50 side with the flange portion 14 of the piston rod 12 interposed therebetween, and the end portions of the piston rod 12 are passed through the respective rod support holes. To do. Then, the front end plate 24 is adjusted so as to close the opening on the load cell 16 side of the cylinder tube 22, and the rear end plate 26 is similarly set so as to close the opening on the displacement sensor 50 side of the cylinder tube 22. Then, the relative positions of the front and rear end plates 24 and 26 are adjusted so that the openings on the manifold 30 side of the control gas flow paths 32 and 34 are aligned on the same plane. When the adjustment is completed, it is confirmed that the control gas flow paths 32 and 34 are fitted between the manifold 30 and the front and rear end plates 24 and 26, and the joint between the cylinder tube 22 and the front and rear end plates 24 and 26 is hermetically sealed. For the hermetic sealing, screwing or the like via a packing such as an O-ring may be used, and when complete hermetic sealing is not required, sealing by a metal mating surface may be used. In this way, an assembly of the housing 20 and the piston rod 12 is obtained, which can be referred to as a piston / cylinder subassembly.

  The manifold 30 is an intermediate member for connecting the gas pressure control valve 40 and the control gas flow paths 32 and 34 of the housing 20, and includes control gas flow paths 33 and 35 corresponding to the control gas flow paths 32 and 34. Such a manifold 30 can be obtained by processing an appropriate metal material or the like. The manifold 30 is tightly connected in an airtight manner so that the control gas flow paths 33 and 35 are aligned with the control gas flow paths 32 and 34 of the piston / cylinder subassembly. For the hermetic connection, screwing using an appropriate hermetic packing or the like can be used.

  The gas pressure control valve 40 is a control valve having a function of generating two controlled gas pressures according to an instruction from a control unit of a tensile / compression tester (not shown). The two controlled gas pressures are supplied to the front and rear gas chambers 36 and 38 inside the housing 20 through the control gas channels 33 and 32 and the control gas channels 35 and 34, respectively. For example, when it is desired to displace the piston rod 12 toward the load cell 16 with a predetermined load, the gas pressure supplied to the gas chamber 38 is made larger than the gas pressure supplied to the gas chamber 36, and the difference in the gas pressures. The gas pressure control valve 40 generates two gas pressures so that a load is obtained by multiplying the pressure by the pressure receiving area of the gas pressure of the flange portion 14. As such a gas pressure control valve, a well-known spool / sleeve type gas pressure control valve or the like can be used.

  Next, the structure of the static pressure gas bearing 100 will be described, particularly the exhaust groove 42 and the shallow groove surface restriction 46 provided in the rod support hole. The static pressure gas bearing 100 is provided at both ends of the piston rod 12, that is, at the front support portion of the piston rod 12 in the front end plate 24 and at the support portion of the rear end plate 26 on the rear side of the piston rod 12. . FIG. 2 is an enlarged view showing a support portion of the piston rod 12 in the rear end plate 26 of the static pressure gas bearings 100 on both sides. Since the front end plate 24 has the same configuration and function, the following description will be made with the rear end plate 26 as a representative. As described above, the inner diameter of the rod support hole is slightly larger than the diameter of the end portion of the piston rod 12, so that the rod support hole 27 is located between the rod support portion 27 of the rear end plate 26 and the piston rod 12, as shown in FIG. There is a gap 58. An exhaust groove 42 and a shallow groove surface constriction 46 are arranged in this order from the end on the rear gas chamber 38 side toward the outside air release 60 side along the gap 58.

  The exhaust groove 42 has a function of collecting the gas leaking from the rear gas chamber 38 through the gap 58 between the rod support portion 27 and the piston rod 12 and flowing it to the exhaust path 44. For example, the gas that has entered the exhaust passage 44 can be returned to the gas pressure control route again. In other words, the exhaust groove 42 has a function of suppressing the unlimited flow of the gas leaking from the rear gas chamber 38 through the gap 58 toward the atmosphere opening 60.

  The shallow groove surface restriction 46 is a plurality of grooves provided on the inner surface of the rod support portion 27, that is, the inner wall of the rod support hole, and has a predetermined width, length, and groove depth in the axial direction. Has the function of floating on the principle of a gas bearing. The length of the groove is set so that one end side is sufficiently spaced apart from the exhaust groove 42 in the axial direction, and the other end is sufficiently spaced from the end on the atmosphere opening 60 side. Then, a slightly deeper groove is provided on the inner wall of the rod support hole connecting the substantially central portions of the shallow groove surface restrictors 46 along the axial direction, and the opening of the gas supply path 48 is connected thereto. A gas having a predetermined supply pressure is supplied to the gas supply path 48 from a gas source (not shown). The shallow groove surface constriction 46 having such a configuration is such that the high-pressure gas from the gas supply path 48 is guided from the opening and flows along the shallow groove, one toward the exhaust groove 42 and the other at the end on the atmosphere opening 60 side. Head to the club. When the shallow groove is cut, it is narrowed toward a narrower gap and flows to the low pressure side, that is, the exhaust groove 42 or the atmosphere opening 60 side, so that a so-called surface throttling device is obtained. Due to this throttling effect, a pressure rise occurs at the throttling portion, and the piston rod 12 is lifted with respect to the rod support portion 27.

The depth of the shallow groove of the shallow groove surface aperture 46 is also related to the size of the gap 58, but in one example, the neutral gap 58 is about 10 μm, and the depth of the shallow groove is about 10 to 15 μm. can do. The gas pressure supplied to the gas supply path 48 can be about 0.5 MPa .

FIG. 3 is a diagram for explaining a portion of the static pressure gas bearing 100 in the rod support portion 27. Here, in order to understand the state of the inner wall of the rod support portion 27 in the rear end plate 26, a sectional view including the central axis of the support hole of the rod support portion 27 is shown for the rear end plate 26 when the piston rod 12 is removed. It is shown. As shown in FIG. 3, lubricating layers 102 and 104 containing MoS ₂ are applied to the inner wall of the rod support portion 27 in the rear end plate 26 constituting the static pressure gas bearing 100. The lubrication layer 104 is in the shallow groove of the shallow groove surface aperture 46 and is slightly thicker than the lubrication layer 102 on the inner wall of the rear end plate 26 other than the shallow groove surface aperture 46, and is therefore shown separately.

The lubricating layers 102 and 104 are thin MoS ₂ layers that function as a buffer when the piston rod 12 and the rear end plate 26 may collide due to impact or the like. The fear of radial impacts is due to sudden changes in characteristics such as fracture of the measurement object during the tensile and compression test, unexpected accidents, impacts at the start and end of operation of the hydrostatic gas bearing 100, etc. Can be considered.

4 is a cross-sectional view in a direction perpendicular to the axial direction of the hydrostatic gas bearing 100 in FIG. Here, the gap between the piston rod 12 and the rear end plate 26 is exaggerated. As shown in the figure, the lubricating layer 106 containing MoS ₂ is also applied to the surface of the piston rod 12. When the static pressure gas bearing 100 is operated, the gap portion between the piston rod 12 and the rear end plate 26 includes the lubricating layers 102 and 104 on the rear end plate 26 side, the lubricating layer 106 on the piston rod 12 side, And a gas layer 59 for rising. In the above example, if the gap 58 in the neutral state is about 10 μm, the gas layer 59 is preferably about 8 μm, and the lubricating layer 102 and the lubricating layer 106 are each preferably about 1 μm.

  FIG. 5 is a view showing the state of the inner surface of the rear end plate 26. As described above, an appropriate metal material is used for the rear end plate 26, and the inner surface of the rod support portion 27 is smoothly finished. However, as shown in FIG. Is a so-called lubricant reservoir having a function of holding the lubricant constituting the lubricant layers 102 and 104. It is preferable that the size of each minute recess 108 has a depth shallower than the thickness of the lubricating layers 102 and 104 and a surface diameter, for example, a diameter smaller than the thickness of the lubricating layers 102 and 104. In the above example, since the thickness of the lubricating layers 102 and 104 is about 1 μm, the depth and diameter of each minute recess 108 are preferably sub-μm. The surface shape of each micro-recess 108 may be other than a circle, such as an ellipse. It should be noted that the minute recess 108 is similarly provided in a portion corresponding to the static pressure gas bearing 100 of the piston rod 12. Such a minute recess 108 can be obtained by a shot peening process in which a minute hard sphere is sprayed on the surface of a metal material or an etching process.

The lubricating layers 102, 104, and 106 are configured to include MoS ₂ as described above. Specifically, the lubricating layers 102, 104, and 106 are manually applied to the surface of the rear end plate 26 or the piston rod 12 so that the MoS ₂ is thin and uniform. It can be obtained by painting with etc. Of course, it may be applied to both the rear end plate 26 and the piston rod 12.

Alternatively, MoS ₂ may be applied to the rear end plate 26 and the piston rod 12 using WPC processing. Here, the WPC treatment is a kind of metal surface treatment, for example, a treatment in which a small shot of 40 to 200 μm is sprayed at a high speed of 100 m / s or more on the material to be treated. It is intended to improve performance. This treatment forms minute irregularities in the material. Here, a lump of fine particles containing MoS ₂ is used for the shot. The lump of fine particles may contain a binder or the like, and preferably a binder having good sliding property or a binder that evaporates due to heat of sliding or the like. That is, a small particle mass of MoS ₂ is uniformly sprayed on the portion of the hydrostatic gas bearing 100 at a high speed, thereby forming a minute recess 108 and attaching a particle mass containing MoS ₂ to that portion. Can be made. The lump of particles containing the attached MoS ₂ is uniformly spread over the entire surface of the hydrostatic gas bearing 100 by the movement of the piston rod 12, and the lubricating layers 102, 104, and 106 containing MoS ₂ are formed. .

As the lubricant for forming the lubricating layers 102, 104, 106, a solid or liquid lubricating material other than MoS ₂ can be used. For example, various general greases used for lubrication of machine parts, lubricating oils having low fluidity, and mixtures of these with MoS ₂ can be used.

  Due to the above configuration, due to sudden changes in characteristics such as fracture of the measurement object during the tensile and compression test, unexpected accidents, radial shocks at the start and end of operation of the hydrostatic gas bearing 100, etc. Before the piston rod 12 and the front and rear end plates 24 and 26 collide, the lubricating layers 102, 104 and 106 function as an impact buffer, and damage to the bearing sliding surface can be prevented. In addition, the presence of the lubricating layer makes the movement of the piston rod 12 smoother, and an accurate tensile compression test can be performed.

  FIG. 6 is a configuration diagram of a piston drive mechanism 80 in which a static pressure gas bearing 110 is provided between the outer periphery of the flange portion 14 of the piston rod 12 and the inner peripheral wall of the cylinder tube 22. FIG. 6 shows the part necessary for explanation in the piston / cylinder subassembly. Elements similar to those in FIG. 1 are denoted by the same reference numerals, and redundant description is omitted. In this piston drive mechanism 80, a static pressure gas bearing by a shallow groove surface restriction 82 is provided on the rod support portion of the front end plate 24, and the shallow groove surface is also provided between the outer periphery of the flange portion 14 and the inner peripheral wall of the cylinder tube 22. A static pressure gas bearing with a throttle 84 is provided.

In the piston drive mechanism 80, a constant high pressure supply pressure Ps is supplied to one of the front and rear gas chambers, and a control gas pressure Pa controlled by an instruction of a control unit of a tension / compression tester (not shown) is supplied to the other. . For example, the supply pressure Ps can be directly supplied from a gas supply source (not shown), and the control gas pressure Pa can be supplied from a gas pressure control valve. In the case of FIG. 6, it is shown that a constant high pressure supply pressure Ps is supplied to the front gas chamber 37. The supply pressure Ps can be set to, for example, about 0.5 MPa .

  FIG. 7 is a view for explaining a portion of the static pressure gas bearing 110 in the rod support portion 27. Here, in order to understand the state of the inner wall of the rod support portion 27 in the front end plate 24, the sectional view including the central axis of the support hole of the rod support portion 27 is shown for the front end plate 24 when the piston rod 12 is removed. It is shown.

  The shallow groove surface restriction 82 provided on the rod support portion 27 of the front end plate 24 is a plurality of grooves provided on the inner wall of the rod support hole, and has a predetermined width, length, and groove depth in the axial direction. The piston rod 12 has a function of floating on the principle of a gas bearing. The axial length of the groove starts from the front gas chamber side end of the rod support 27 and can be about 1/2 to 2/3 of the length of the rod support 27. The shallow groove surface constriction 82 having such a structure is flowed along the shallow groove when the high-pressure gas from the front gas chamber 37 is pushed in, and proceeds toward the end on the atmosphere opening 60 side. And when the shallow groove is cut, it is squeezed toward a narrower gap and flows to the low pressure side, so that it becomes a so-called surface squeezing device. Due to this throttling effect, a pressure rise occurs at the throttling portion, and the piston rod 12 is lifted with respect to the rod support portion 27.

As shown in FIG. 7, lubricating layers 112 and 114 containing MoS ₂ are applied to the inner wall of the rod support portion 27 in the front end plate 24 constituting the static pressure gas bearing 110. The lubricating layer 114 is in the shallow groove of the shallow groove surface restrictor 82 and is slightly thicker than the lubricating layer 112 on the inner wall of the rear end plate 26 other than the shallow groove surface restrictor 46, and is therefore shown separately. The contents of the lubricating layers 112 and 114 are the same as those described with reference to FIGS. Although not shown, a similar lubricating layer is also applied to the surface of the piston rod 12.

  FIG. 8 is a view for explaining a portion of the static pressure gas bearing 110 on the outer periphery of the flange portion 14. Here, the state when the piston rod 12 is removed from the housing 20 is shown so that the state of the outer surface of the flange portion 14 of the piston rod 12 can be seen.

  A shallow groove surface stop 84 is provided on the outer periphery of the flange portion 14. In this connection, an exhaust groove 86 is also provided on the outer periphery of the flange portion 14, and the exhaust groove 86 is connected to an exhaust path 88 that passes through the piston rod 12. The exhaust path 88 can be opened to the atmosphere. The shallow groove surface restriction 84 is a plurality of grooves provided on the outer periphery of the flange portion 14 and has a predetermined width, length, and groove depth in the axial direction, and causes the piston rod 12 to float on the principle of a gas bearing. It has a function. The axial length of the groove starts from the front gas chamber side end of the flange portion 14 and can be about ½ of the axial length of the flange portion 14.

  The shallow groove surface constriction 84 having such a configuration is directed to the exhaust groove 86 that is pressurized with the high-pressure gas from the front gas chamber 37 and flows along the shallow groove, and is finally released to the atmosphere. And when the shallow groove is cut, it is squeezed toward a narrower gap and flows to the low pressure side, so that it becomes a so-called surface squeezing device. Due to this throttling effect, a pressure rise occurs at the throttling portion, and the piston rod 12 is lifted with respect to the rod support portion 27.

  The depth of the shallow grooves of these shallow groove surface restrictors 82 and 84 is, for example, about the gap between the piston rod 12 and the inner wall surface of the cylinder tube 22 facing the same, as in the shallow groove surface restrictor of FIG. The depth of the shallow groove can be about 3 to 20 μm as 10 μm.

As shown in FIG. 8, lubricating layers 112 and 114 containing MoS ₂ are applied to the outer peripheral surface of the flange portion 14 constituting the static pressure gas bearing 110. The lubricating layer 114 is in the shallow groove of the shallow groove surface restrictor 84 and is slightly thicker than the lubricating layer 112 on the outer peripheral surface of the flange portion 14 other than the shallow groove surface restrictor 84, and is therefore shown separately. The contents of the lubricating layers 112 and 114 are the same as those described with reference to FIGS. Although not shown, a similar lubricating layer is also applied to the surface of the cylinder tube 22.

  With the above configuration, before the piston rod 12 and the front end plate 24 or the cylinder tube 22 collide with each other during a tensile compression test and a radial impact at the start and end of the operation of the hydrostatic gas bearing 100. The lubricating layers 112, 114, and 116 function as an impact buffer and can prevent the bearing sliding surface from being damaged. In addition, the presence of the lubricating layer makes the movement of the piston rod 12 smoother, and an accurate tensile compression test can be performed.

It is a figure which shows the structure of the piston drive mechanism for tension compression test machines in which the static pressure gas bearing in embodiment which concerns on this invention is used. It is an enlarged view which shows the support part of the piston rod in a rear end plate among the static pressure gas bearings in embodiment which concerns on this invention. It is a figure explaining the part of the static pressure gas bearing in the rod support part in embodiment which concerns on this invention. It is sectional drawing in the direction perpendicular | vertical to the axial direction of the static pressure gas bearing in FIG. In embodiment which concerns on this invention, it is a figure which shows the mode of the inner surface of a rear end plate. In other embodiment, it is a block diagram of the piston drive mechanism which provided the static pressure gas bearing. In other embodiment, it is a figure explaining the part of the static pressure gas bearing in a rod support part. In other embodiment, it is a figure explaining the part of the static pressure gas bearing in the outer periphery of a flange part.

Explanation of symbols

  10, 80 Piston drive mechanism, 12 Piston rod, 14 Flange, 16 Load cell, 20 Housing, 22 Cylinder tube, 24, 26 Front and rear end plates, 27 Rod support, 30 Manifold, 32, 33, 34, 35 Control gas flow Path, 36, 37, 38 Front and rear gas chambers, 40 Gas pressure control valve, 42, 86 Exhaust groove, 44, 88 Exhaust path, 48 Gas supply path, 50 Displacement sensor, 52 Soft magnetic probe, 54 Transformer winding, 56 Stopper, 58 Clearance, 59 Gas layer, 60 Open to atmosphere, 100, 110 Static pressure gas bearing, 102, 104, 106, 112, 114, 116 Lubricating layer, 108 Small indentation.

Claims (5)

In a static pressure gas bearing that supports the rectilinear axis of the piston drive mechanism in a levitating manner with respect to the housing,
A solid or liquid lubricating layer for shock buffer provided on the gas receiving surface of the straight shaft and the gas receiving wall of the housing ;
A plurality of lubricant reservoirs provided in at least one of the gas receiving surface or the gas receiving wall and having a depth shallower than the thickness of the lubricating layer and a surface diameter smaller than the thickness of the lubricating layer;
A static pressure gas bearing for a piston drive mechanism characterized by comprising: In the static pressure gas bearing of the piston drive mechanism according to claim 1,
A shallow groove that is provided along the axial direction on the inner surface of the housing that supports the linear axis of the piston drive mechanism, and that allows the gas supplied from the gas supply path to flow and floats the linear axis relative to the housing. Including a surface aperture,
A static pressure gas bearing for a piston drive mechanism, wherein the lubricating layer is provided on the gas receiving wall of the housing including the surface of the shallow groove surface restrictor and the gas receiving surface of the linear axis facing the housing . In the static pressure gas bearing of the piston drive mechanism according to claim 1,
A static pressure gas bearing for a piston drive mechanism, wherein the lubricating layer is configured to contain grease. In the static pressure gas bearing of the piston drive mechanism according to claim 1,
The lubricating layer is composed of molybdenum disulfide by WPC treatment, and is a static pressure gas bearing for a piston drive mechanism.   A gas pressure actuator comprising the static pressure gas bearing of the piston drive mechanism according to any one of claims 1 to 4.

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