JP4451757B2 - Piston drive mechanism - Google Patents

Description

  The present invention relates to a piston drive mechanism including a piston and a cylinder, and more particularly to a piston drive mechanism in which a piston is driven in the axial direction by gas pressure.

  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. A drive mechanism using a piston and a cylinder is devised so that fluid pressure is not lost due to movement of the piston in the axial direction. For example, precise dimensional control, a seal ring, and the like are used for the sliding portion between the cylinder inner wall and the piston outer diameter.

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.

  However, the conventionally known piston drive mechanism is accurately guided in the axial direction by a sliding portion with good dimensional accuracy so that fluid pressure does not leak. Therefore, a load such as friction of the sliding portion is applied, and there may be a limit to smooth operation and displacement, and high-precision control of the load.

  In addition, in these test machines, depending on the nature of the test object, when a load is applied in the axial direction, slipping or the like occurs, so that an external force in the radial direction is applied to the load shaft, and the load shaft, that is, the piston shaft. May become diagonal. In the conventional piston drive mechanism, the fluid pressure is maintained by accurately guiding the movement in the axial direction. Therefore, if an external force that causes the piston shaft to be inclined is received, the fluid pressure cannot be maintained, and the displacement or Precise control of the load becomes difficult. In addition, the sliding surface between the piston and the cylinder may be damaged or deformed, making it difficult to perform a test operation.

  An object of the present invention is to provide a piston drive mechanism that allows a piston to tilt in the axial direction. Another object is to provide a piston drive mechanism that can move with high accuracy.

1. About the concept of precursor length In studying how to suppress the influence of gas leakage, which is a problem when the piston is tilted in the axial direction in the piston drive mechanism, I came up with the concept of precursor length. . Therefore, the precursor length will be described below.

The precursor length is a distance from the channel inlet where the uniform velocity distribution at the channel inlet becomes a parabolic distribution with respect to the channel cross section when the fluid flows through the narrow channel. For example, the following statement is made in Tetsufumi Okamoto, Applied Fluid Dynamics, Seibundo Shinkosha, February 10, 1966, 8th edition, p106. That is, when a fluid flows through the circular pipe, a uniform velocity distribution is obtained at the inlet of the circular pipe, and gradually becomes a parabolic distribution as it travels through the flow path. Strictly speaking, when the entrance is set to x = 0, the parabolic distribution is reached at x = ∞, but in reality, an object very close to the parabolic distribution is obtained at finite x. Therefore, taking the place where the velocity at the center of the tube has a difference of only 1% from the velocity at the center of the parabola distribution at x = ∞, the distance from the entrance to this point is called the precursor length or the run-up distance. The formula for calculating the precursor length is represented by, for example, x ₁ = 0.26a × R ₁ . Here, x ₁ is the precursor length, a is the tube radius, and R ₁ is the Reynolds number.

  Thus, the precursor length is the distance from the inlet on the flow path where the velocity distribution is substantially the same as the parabolic distribution at infinity of the flow path when the fluid flows through the narrow flow path. When this is applied to the gas flow leaking from the gas chamber inside the cylinder to the outside atmosphere through the gap between the cylinder and the piston rod in the piston drive mechanism, the gap between the cylinder and the piston rod is defined as d and flows through the gap d. If the Reynolds number of the gas flow is Re, the precursor length is proportional to d × Re. The proportionality constant α can be obtained experimentally in each piston drive mechanism. Using the obtained α, the distance from the inlet is αd × Re becomes the precursor length position.

  If the piston rod is allowed to be inclined with respect to the axial direction, the gap between the inner diameter of the rod support portion and the piston rod cannot be set strictly, and momentum passes through the gap from the gas chamber in the cylinder housing. As a result, it is expected that leakage will increase toward the outside atmosphere. Leakage will increase if the exhaust port is located too close to the gas chamber. Moreover, even if it is provided too far, the apparatus becomes large.

  Thus, the idea of the precursor length was conceived by considering where to provide an exhaust port without increasing the size of the apparatus and reducing the amount of gas that leaks efficiently. That is, the position of the precursor length is the same as that at the position at infinity when viewed from the entrance, and the wall resistance of the leaking gas is maximized. Therefore, by providing the position of the exhaust port in the vicinity of the position of the precursor length or farther from the gas chamber, the amount of leaking gas can be reduced efficiently without increasing the size of the apparatus. .

2. The piston drive mechanism according to the present invention has a gas receiving plate part that partitions the inside of a cylinder housing into front and rear gas chambers, and an end protrudes from the cylinder housing, and is supplied to each of the front and rear gas chambers. A piston rod that is driven by two control gas pressures that are moved in the axial direction, and a gas supply path in which an opening is provided in a rod support portion of a cylinder housing that supports the piston rod so as to be movable in the axial direction. A gas is supplied between the inner diameter of the support part and the piston rod, and the rod support part gas supply path for supporting the piston rod by floating in the radial direction with respect to the cylinder housing; It is provided at a position inside the body and leaks from any of the front and rear gas chambers inside the cylinder housing through the gap between the inner diameter of the rod support and the piston rod. A rod support portion exhaust groove for exhausting gas and gas from the rod support portion gas supply path, and the rod support portion exhaust groove has a gap d through which a gas flow between the inner diameter of the rod support portion and the piston rod flows. And the difference between the gas pressure difference between the higher gas pressure of the two control gas pressures supplied to the front and rear gas chambers and the exhaust gas pressure in the rod support portion exhaust groove, and the clearance d. The flow velocity of the gas flow is V, the density of the gas flow through the gap d is ρ, the viscosity coefficient is μ, the Reynolds number calculated by Vdρ / μ is Re, and the gap between the inner diameter of the rod support portion and the piston rod is previously set. The proportional constant obtained by experiment for the precursor length of the flow of the rod is α, and the distance along the axial direction from the end on the cylinder housing inner side in the rod support portion is outside the precursor length position of αd × Re and the rod support Part Characterized in that it is arranged from the body supply passage inner position.

Moreover, it is preferable that a rod support part gas supply path supplies gas between the surface restriction | limiting of the shallow groove | channel provided in the internal diameter of a rod support part, and a piston rod.

  Moreover, it is preferable that a gas receiving plate part is comprised including the flange part of a piston rod, and the bellophram which connects between a cylinder housing | casing and a flange part flexibly and airtightly.

Further, a piston drive mechanism according to the present invention, a gas receiving plate portion gas exhaust passage opening is provided in the receiving plate sliding portion formed between the outer periphery and the inner wall of the cylinder housing of the gas-body receiving plate portion, the receiving plate A surface restriction of a shallow groove that is provided in the sliding part and faces the gas exhaust air passage of the gas receiving plate , and squeezes the gas from the gas chamber inside the cylinder housing through the shallow groove toward the gas exhaust air passage of the gas receiving plate. The surface plate for levitation of the gas receiving plate part that floats and supports the inner wall of the cylinder case and the rod support part of the cylinder case that supports the piston rod so that it can move in the axial direction. The surface restriction of the shallow groove, which is made to flow from the gas chamber inside the cylinder housing through the shallow groove toward the outside air side end of the rod support portion, thereby allowing the piston rod to move against the inner wall of the cylinder housing. A surface diaphragm for floating the rod that is levitated and supported; Characterized in that it comprises.

  In the piston drive mechanism according to the present invention, it is preferable that the piston drive mechanism includes a metal bearing or a composite material bearing that is attached to the cylinder housing and restricts displacement in the radial direction of the piston rod.

  According to the above configuration, since the gas supply path is provided to float and support the piston rod in the radial direction with respect to the cylinder housing, the piston rod can be moved smoothly and accurately with respect to the cylinder housing.

  Moreover, since the exhaust port is arranged at a position outside the precursor length, the gas leaking from the gas chamber can be efficiently recovered. Therefore, it is possible to reduce the influence of gas leakage while allowing the piston to tilt in the axial direction.

  In addition, a shallow groove surface restriction is provided on the inner diameter of the rod support, and gas is supplied between this shallow groove and the piston rod from the gas supply path, so that the piston rod can be lifted by the shallow groove restriction effect with a simple structure. Can be made.

  Further, since the flange portion of the piston rod and the cylinder housing are connected by a bellophram, the front and rear gas chambers are partitioned airtightly by the flange portion and the bellophram even if the piston is inclined in the axial direction. Therefore, even if the piston rod is tilted in the axial direction, leakage of gas pressure between the front and rear gas chambers can be prevented.

  In addition, a surface diaphragm for floating the receiving plate part is provided in the sliding part of the receiving plate, a surface diaphragm for floating the rod is provided in the rod support part, and one from the gas chamber inside the cylinder housing is for floating the receiving plate part. Since the gas flows through the surface restriction to the gas exhaust passage and the other through the surface restriction for floating the rod to the external atmosphere, the receiving plate sliding part and the rod support part have a simple configuration. Can lift the piston rod. Therefore, the piston rod can be moved smoothly and accurately with respect to the cylinder housing.

  In addition, because the cylinder housing is provided with a metal bearing that regulates the displacement of the piston rod in the radial direction, the limit is determined by the metal bearing even if the piston is inclined in the axial direction. Can be prevented from being damaged due to an unexpected collision between the two.

  As described above, according to the piston drive mechanism according to the present invention, the piston can be allowed to tilt in the axial direction. Further, the piston can be moved with high accuracy.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the following, the piston drive mechanism used in the tensile / compression test machine will be described. However, the object to which the piston drive mechanism is applied is not limited to such a test machine, and it is necessary to allow the piston to be inclined with respect to the shaft method. Any device can be equally applicable.

  FIG. 1 is a diagram showing a configuration of a piston drive mechanism 10 used in a tensile / compression tester. The piston drive mechanism 10 includes a piston rod 12, a cylinder 20, and a gas pressure control valve 40 that supplies a controlled gas pressure. A manifold 30 is provided between the gas pressure control valve 40 and the cylinder 20, and the gas pressure controlled by the gas pressure control valve 40 is guided into the cylinder 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, divides the inside of the cylinder 20 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. As described above, the piston drive mechanism 10 used in the tension / compression tester moves the piston rod 12 in the axial direction by the gas pressure, and the test is not shown through the load cell 16 provided at the tip of the piston rod 12. It has a function of applying a load to an 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 cylinder 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 by the cylinder 20 so as to be freely movable in the axial direction, but it is preferable that the portions are similarly subjected to a sufficiently smooth surface treatment and an appropriate hardening 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, the material can be processed into a flanged cylinder and subjected to surface hardening treatment, surface polishing treatment, lubrication plating treatment, and 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 tip of the other side of the piston rod 12 is extended to attach the soft magnetic probe 52, and a transformer winding 54 that cooperates with this is provided on the cylinder 20 side. 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 cylinder 20 is a one-time airtight housing that has a function of accommodating the flange portion 14 of the piston rod 12 therein, 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 tight in terms of the performance of the tension / compression tester except when the piston rod 12 is abnormally inclined in the axial direction. The cylinder 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 are respectively applied to the openings on both sides of the substantially annular cylinder tube 22 to constitute a cylinder housing as a whole.

  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 inner periphery of the material can be processed into a predetermined dimension and subjected to surface hardening treatment, surface polishing treatment, lubrication plating treatment, and the like.

  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 for supporting the piston rod 12 through the center, and have a function of closing both side openings of the cylinder tube 22. The inner diameter of the rod support hole is slightly larger than the diameters at both ends of the piston rod 12. An exhaust groove 42, a shallow groove surface stop 46, and the like are provided at the rod support hole. Details of these 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 cylinder 20 via 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.

  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. In this way, an assembly of cylinder 20 and 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, 34 of the cylinder 20, and includes control gas flow paths 33, 35 corresponding to the control gas flow paths 32, 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 cylinder 20 through the control gas passages 33 and 32 and the control gas passages 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 exhaust groove 42 and the shallow groove surface stop 46 provided in the rod support hole will be described. FIG. 2 is an enlarged view showing a support portion of the piston rod 12 in the rear end plate 26. 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.

  The exhaust groove 42 is disposed along the axial direction of the rod support portion 27 at a position where the distance from the end of the rear gas chamber 38 is equal to or longer than the so-called precursor length. Here, the precursor length is the distance from the channel inlet where the uniform velocity distribution at the channel inlet becomes substantially parabolic with respect to the channel cross section when the fluid flows through the narrow channel as described above. It is. FIG. 3 shows the relationship between the change in the flow velocity distribution of the gas flowing through the gap 58 and the precursor length. As shown in FIG. 3, the velocity distribution 62 that is uniform at the entrance of the gap 58, that is, at the end on the rear gas chamber 38 side, gradually changes in distribution shape as it travels through the gap 58, and advances at infinity. Parabolic distribution. The velocity at the center of the precursor length becomes a velocity distribution 64 very close to the parabola distribution having a difference of 1% from the velocity at the center of the parabola distribution at infinity. Now, assuming that the size of the gap 58 is d, the Reynolds number of the gas flow through the gap 58 is Re, and the proportionality constant determined in the experiment is α, the precursor length = αd × Re. The Reynolds number is represented by Re = VDρ / η, where V is the flow velocity of the fluid, η is the viscosity coefficient, ρ is the density, and D is the channel dimension.

  For example, if Re = 2000 and d = 10 to 20 μm, the precursor length is about 5 mm. The exhaust groove 42 is disposed at a position farther from the position of the precursor length when viewed from the end of the rear gas chamber 38. With such a configuration, the gas leaking through the gap 58 can be efficiently collected with the same effect as the exhaust groove 42 viewed from the end of the rear gas chamber 38 at an infinite distance. Can be downsized.

  The shallow groove surface restriction 46 is a plurality of grooves provided on the inner surface of the rod support portion 57, 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, the opening of the gas supply path 48 is connected to a substantially central portion of the length along the axial direction of each shallow groove surface stop 46. 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 ejected 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. 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 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 3 to 20 μm. can do. Moreover, the gas pressure supplied to the gas supply path 48 can be set to about 0.5 Mpa.

  The operation of the piston drive mechanism 10 for a tensile and compression tester having such a configuration will be described. As an example, the case where the stress-strain characteristic of the test object is precisely measured will be taken up. First, after initializing the tensile / compression tester, a test object is set between the tip of the load cell 16 and the stage of the tester (not shown). Then, a control unit (not shown) of the tensile and compression tester instructs the gas pressure control valve 40 to generate a load at a predetermined application speed. For example, an instruction is issued so that a load is applied to the tip of the piston rod 12 at an application speed of 1 N / sec. Prior to this, supply of high-pressure gas at a predetermined supply pressure to a gas source (not shown) from the control unit of the tension / compression tester is performed with respect to the gas pressure control valve 40 and the gas supply path 48 of the cylinder 20. Instructed to do so, and an instruction to suck the exhaust passage 44 of the cylinder 20 at a predetermined exhaust pressure is issued to an exhaust device (not shown).

  The gas pressure control valve 40 uses the feedback signals from the load cell 16 and the displacement sensor 50 to generate two controlled gas pressures according to a predetermined gas pressure generation algorithm so as to achieve an instructed application speed. The controlled gas pressure is supplied to the front and rear gas chambers 36 and 38 via the control gas flow paths 33, 32, 35 and 34. The flange portion 14 of the piston rod 12 receives the gas pressure in the front and rear gas chambers 36 and 38, and maintains a normal space between the outer periphery of the flange portion 14 and the inner peripheral wall of the cylinder tube 22 according to the differential pressure, It is driven to move in the axial direction. That is, if the instruction of the tension / compression tester is pulling at an application speed of 1 N / sec, it is moved to the displacement sensor 50 side in the X direction of FIG. The load and displacement of the moving drive are monitored by the load cell 16 and the displacement sensor 50 as described above.

  In this way, a load can be applied to the test object at a predetermined application speed by moving the piston rod 12. The stress-strain characteristics of the test object can be obtained from the output unit of a tensile / compression tester (not shown) using the output data of the load cell 16 and the displacement sensor 50.

  The piston rod 12 is lifted in the radial direction from the rod support portion 27 and driven to move in the axial direction by the drawing effect of the shallow groove surface restriction 46 of the front and rear end plates 24 and 26. In addition, the gas flowing from the front and rear gas chambers 36 and 38 toward the atmosphere opening 60 through the levitation gap is effectively collected by the exhaust groove 42 and the exhaust passage 44 disposed farther from the precursor length. Therefore, the piston rod 12 can move smoothly without receiving the frictional load on the rod support 27 while suppressing the influence of leakage of the gas pressure in the front and rear gas chambers 36 and 38 from the rod support 27, so that high-precision measurement is possible. Is possible.

  Further, the support of the piston rod 12 in the rod support portion 27 is a gas bearing mechanism having a degree of freedom with respect to the displacement of the piston rod 12 in the radial direction, and the gas that leaks through the floating gap of the gas bearing by the action of the exhaust groove 42. Therefore, the piston rod 12 can be allowed to tilt from the axial direction within a certain range due to the characteristics of the test object during the tensile and compression test.

  In a piston drive mechanism for a tension / compression tester, the piston rod may tilt from the axial direction due to the nature of the object to be measured, but if it is tilted too much, the piston rod will collide with the cylinder inner wall or the inner wall of the rod support. May cause damage.

  FIG. 4 is a configuration diagram of a piston drive mechanism 70 that can suppress an excessive inclination of the piston rod 12. FIG. 4 shows the parts 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 the piston drive mechanism 70, metal bearings 72 and 74 are provided at the ends of the front and rear end plates 24 and 26 on the atmosphere release 60 side, respectively. The metal bearing may be provided at one place on the side to which the load is applied.

  The metal bearings 72 and 74 are ring-shaped bearings made of a metal material or a composite material rich in lubricity, and the inner diameter thereof is larger than the diameter of the end portion of the piston rod 12, and the front and rear end plates 24 and 26. It is set smaller than the diameter of the rod support hole. The metal bearings 72 and 74 are attached to the ends of the front and rear end plates 24 and 26 on the atmosphere opening 60 side so as to be concentric with the rod support holes of the front and rear end plates 24 and 26. Attachment can be performed by screwing or fixing by fitting. Such metal bearings 72 and 74 can be obtained by processing a soft metal such as brass or copper, a porous metal impregnated with a lubricating oil, or a composite material into a predetermined ring shape.

  In the piston drive mechanism 70 having such a configuration, even if the piston rod 12 is displaced in the radial direction, the R direction shown in FIG. Since it is smaller than the inner diameter of the rod support portion of the end plates 24 and 26, the outer shape of the piston rod 12 first hits the metal bearings 72 and 74 having lubricity when excessively displaced or inclined. Therefore, the outer periphery of the flange portion 14 of the piston rod 12 collides with the inner peripheral wall of the cylinder tube 22, or the end portion of the piston rod 12 collides with the shallow groove surface restriction 46 of the rod support portion of the front and rear end plates 24, 26. It is possible to prevent them from being damaged.

  In a piston drive mechanism for a tension / compression tester, the piston rod may tilt from the axial direction due to the nature of the object to be measured, but if it tilts too much, the flange of the piston rod completely partitions the front and rear gas chambers in the cylinder. I can't.

  FIG. 5 is a configuration diagram of the piston driving mechanism 76 that can partition the front and rear gas chambers in an airtight manner regardless of the inclination of the piston rod 12 in the axial direction. FIG. 5 shows the parts 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 the piston drive mechanism 76, a flexible and airtight bellowram 78 is provided between the flange portion 15 of the piston rod 12 and the cylinder tube 22.

  The belofram 78 is a flexible ring member that secretly partitions between the outer periphery of the flange portion 15 and the inner peripheral wall of the cylinder tube 22. For example, it is possible to use a thin metal plate bent to have an appropriate shape so as to have flexibility. The outer peripheral portion of the ring-shaped member having such a bend is fixed to the cylinder tube 22, and the inner peripheral portion is fixed to the flange portion 15. The number of beloframs may be one or more. In this case, the diameter of the flange portion 15 may be made considerably smaller than the inner diameter of the cylinder tube 22 as long as a surface that receives the gas pressure can be secured.

  In the piston drive mechanism 76 having such a configuration, even if the piston rod 12 is displaced in the radial direction, the R direction shown in FIG. Further, since the bellophram 78 is airtight even if it is displaced or deformed, the front and rear gas chambers 36 and 38 are not in fluid communication with each other, and the front and rear gas chambers can be completely partitioned in the cylinder. Enables precise measurement in a compression tester.

  FIG. 6 is a configuration diagram of a piston drive mechanism 80 in which a gas bearing mechanism is also 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 gas bearing mechanism using a shallow groove surface restriction 82 is provided on the rod support portion of the front end plate 24, and the shallow groove surface restriction is also provided between the outer periphery of the flange portion 14 and the inner peripheral wall of the cylinder tube 22. 84 is provided with a gas bearing mechanism.

  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 about 0.5 Mpa, for example.

  FIG. 7 is a view showing a state of the shallow groove surface aperture 82 provided on the rod support portion 27 of the front end plate 24. 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.

  FIG. 8 is a view showing a state of the shallow groove surface stop 84 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. Then, when the shallow groove is cut, it is squeezed toward a narrower gap and flows to the low pressure side, so that a so-called surface squeezing 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 shallow groove depths of these shallow groove surface restrictors 82 and 84 are set such that the gap between the piston rod 12 and the inner wall surface of the cylinder 20 facing the piston rod 12 is about 10 μm, as in the shallow groove surface restrictor of FIG. The depth of the shallow groove can be about 3 to 20 μm.

  In the piston drive mechanism 80 having such a configuration, two types of gas bearing mechanisms can be created from one gas chamber 37, and the piston rod can be smoothly moved and driven with a simple configuration. Is possible.

It is a figure which shows the structure of the piston drive mechanism in embodiment based on this invention used for the tension compression tester as an application example. In embodiment which concerns on this invention, it is an enlarged view which shows the support part of the piston rod in a rear end plate. In embodiment which concerns on this invention, it is a figure explaining the change of the flow velocity distribution of gas, precursor length, and the arrangement | positioning relationship of an exhaust groove. It is a piston drive mechanism block diagram of other embodiment. It is a block diagram of the piston drive mechanism in other embodiment. It is a block diagram of the piston drive mechanism in another embodiment. In another embodiment, it is a figure which shows the mode of the shallow groove | channel surface aperture | diaphragm | restriction provided in the rod support part of a front end plate. In another embodiment, it is a figure which shows the mode of the shallow groove | channel surface constriction provided in the outer periphery of a flange part.

Explanation of symbols

  10, 70, 76, 80 Piston drive mechanism, 12 Piston rod, 14, 15 Flange, 16 Load cell, 20 Cylinder, 22 Cylinder tube, 24, 26 End plate, 27 Rod support, 30 Manifold, 33, 32, 35 , 34 Control gas flow path, 36, 37, 38 Gas chamber, 40 Gas pressure control valve, 42, 86 Exhaust groove, 44, 88 Exhaust path, 46, 82, 84 Shallow groove surface restriction, 48 Gas supply path, 50 Displacement Sensor, 52 Soft magnetic probe, 54 Transformer winding, 56 Stopper, 57 Rod support, 58 Clearance, 60 Open to atmosphere, 62, 64 Speed distribution, 72, 74 Metal bearing, 78 Bellofram.

Claims (5)

A rod having a gas receiving plate for partitioning the inside of the cylinder housing into front and rear gas chambers, and an end projecting from the cylinder housing, which is driven by two control gas pressures supplied to the front and rear gas chambers. A piston rod moving in the direction,
A gas supply path in which an opening is provided in a rod support portion of a cylinder housing that supports the piston rod so as to be movable in the axial direction, and gas is supplied between the inner diameter of the rod support portion and the piston rod to the cylinder housing. A rod support part gas supply passage for floating and supporting the piston rod in the radial direction;
It is provided at a position further inside the cylinder housing than the rod support portion gas supply path, and leaks from one of the front and rear gas chambers inside the cylinder housing through the gap between the inner diameter of the rod support portion and the piston rod. Rod support part exhaust groove for exhausting gas from the coming gas and rod support part gas supply path;
With
The rod support part exhaust groove
The gap through which the gas flow between the inner diameter of the rod support and the piston rod flows is d,
Gas flow required based on the difference in gas pressure between the higher gas pressure of the two control gas pressures supplied to the front and rear gas chambers and the exhaust gas pressure in the rod support portion exhaust groove, and the gap d Let V be the flow velocity of
The density of the gas flow flowing through the gap d is ρ, the viscosity coefficient is μ, the Reynolds number calculated by Vdρ / μ is Re,
Α is a proportionality constant obtained in advance for the precursor length of the flow in the gap between the inner diameter of the rod support and the piston rod,
The distance along the axial direction from the end on the cylinder housing inner side in the rod support part is arranged outside the αd × Re precursor length position and inside the rod support part gas supply path. Piston drive mechanism. The piston drive mechanism according to claim 1,
The rod support portion gas supply path supplies a gas between a surface throttle of a shallow groove provided on the inner diameter of the rod support portion and the piston rod. The piston drive mechanism according to claim 1 or 2,
The gas receiving plate portion includes a flange portion of a piston rod, and a bellophram that is flexible and airtightly connected between the cylinder housing and the flange portion. The piston drive mechanism according to claim 1,
A gas receiving plate portion gas exhaust passage in which an opening is provided in a receiving plate sliding portion formed by the outer periphery of the gas receiving plate portion and the inner wall of the cylinder housing;
A surface restriction of a shallow groove provided in the receiving plate sliding portion and directed to the gas receiving plate portion gas exhaust passage, and gas from the gas chamber inside the cylinder housing through the shallow groove toward the gas receiving plate portion gas exhaust passage. By squeezing and flowing, the surface diaphragm for floating the receiving plate portion that supports the gas receiving plate portion that floats and supports the inner wall of the cylinder housing,
This is a shallow groove surface throttle provided in the rod support part of the cylinder housing that supports the piston rod so as to be movable in the axial direction, passing from the gas chamber inside the cylinder housing to the outside air side end of the rod support part. By squeezing and flowing the gas toward the surface, a surface squeeze for levitation of the rod that floats and supports the piston rod against the inner wall of the cylinder housing,
A piston drive mechanism comprising: In the piston drive mechanism according to any one of claims 1 to 4,
A piston drive mechanism comprising a metal bearing or a composite bearing attached to a cylinder housing and restricting displacement in a radial direction of a piston rod.

Images