JP2013130260A - Liquid static pressure linear motion guide device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize a structure that can suppress attitude change when a movable body 2 moves without upsizing and complicating a device.SOLUTION: Positions of liquid supply holes 7 in respective recessed parts 4 are arranged so as to satisfy a following condition: a summation of distances between a centroid G of a movable body 2 and respective liquid supply points P as geometric centroids of the liquid supply holes 7 of the respective recessed parts 4 in respective moving directions is larger than a summation of distances between the centroid G of the movable body 2 and centers N of the respective recessed parts 4 in the respective moving directions. Accordingly, a fluctuation of moment of the movable body 2 at moving is restrained and thereby attitude change thereof can be suppressed.

Description

  The present invention relates to a liquid hydrostatic linear motion guide device including a liquid hydrostatic bearing, which is used in, for example, an ultraprecision machine.

  As a linear motion guide device, a liquid static pressure linear motion guide device including a liquid static pressure bearing is known. The hydrostatic bearing forms a lubricating fluid film by forcibly supplying a pressurized fluid to the bearing gap between the bearing surface of the movable body and the guide surface of the guide member, and the pressure of the lubricating fluid film This is a bearing that floats a movable body in a non-contact manner. In a liquid hydrostatic bearing that uses a liquid as a working fluid, in many cases, as shown in FIG. 8 (a), the movable body 2 is formed with a recess 4 that opens to the bearing surface 3 (oblique lattice region). . In addition, as shown in FIG.8 (b), the part remove | excluding the opening surface 5 (satin surface area | region) of the recessed part 4 from the bearing surface 3 is called the land 6 (lattice area | region). Therefore, the bearing surface 3 is composed of the opening surface 5 of the recess 4 and the land 6.

  The opening surface 5 of the recess 4 is included in the land 6. As shown in FIG. 9A, the recess 4 has a sufficient depth with respect to the bearing gap 8 formed by the land 6 and the guide surface 1. have. By providing the recess 4, the bearing surface 3 can be filled with a pressurized fluid without causing a pressure drop. For this reason, as can be seen by comparing FIGS. 9A and 9B, compared with the case where the recess 4 is not provided, a larger integrated value of the pressure, that is, the levitation force is obtained with the liquid hydrostatic bearing of the same size. I can do things.

  However, when the concave portion 4 is provided, the posture of the movable body 2 may be inclined when the movable body 2 moves. That is, as shown in FIG. 9C, when the movable body 2 moves in the left direction in the figure, the flow rate throttled on the right side in the figure of the bearing gap 8 increases because the recess 4 is a fluid pool. As a result, a pressure gradient is generated in which the pressure increases on the right side in the drawing, that is, behind the movable body moving direction. Accordingly, the moment around the center of gravity of the movable body 2 that is balanced when the movable body 2 is stationary fluctuates in the direction of lifting the rear portion in the movement direction due to the movement of the movable body 2, causing a change in the posture of the movable body 2.

  Normally, in a liquid hydrostatic linear motion guide device equipped with a liquid hydrostatic bearing, it is common to counteract fluctuations and biases in the pressure distribution by disposing bearings of the same type and shape so as to sandwich the movable body. Is. On the other hand, when the same type and shape bearings are not arranged opposite to each other, as a prior art for suppressing the change in the posture of the movable body, the inclination of the movable body is detected and the pressure of the fluid supplied to the static pressure guide surface is changed. The structure to be made is proposed (patent document 1).

JP 62-241629 A

  However, the opposing arrangement of hydrostatic bearings, which is a common method, leads to an increase in size of the apparatus and difficulty in processing and assembly. On the other hand, in the case of the technique described in Patent Document 1, since the device for detecting the inclination and the means for correcting the inclination are provided, the apparatus becomes complicated and large.

  In view of such circumstances, the present invention was invented to realize a structure capable of suppressing a change in posture during movement of a movable body without causing an increase in size and complexity of the apparatus.

  The present invention has a guide member having a guide surface and a bearing surface that constitutes a hydrostatic bearing between the guide surface and is arranged in a state where a pressurized pressure is applied toward the guide surface, A liquid static pressure linear motion guide apparatus comprising: a movable body that moves along a guide member; and a liquid supply means that supplies a liquid between the bearing surface and the guide surface. A plurality of surfaces are arranged side by side in the moving direction, and the plurality of bearing surfaces are respectively disposed on a recess opening toward the guide surface and on the bottom surface or wall surface of the recess, and liquid is supplied from the liquid supply means. Liquid supply holes are formed, and the plurality of liquid supply holes are arranged in the respective moving directions of the liquid supply point serving as the geometric center of gravity of the liquid supply hole in each of the recesses and the center of gravity of the movable body. The total distance is the center of the recess and the movable Than the respective sum of the distance of the movement direction between the center of gravity of which is arranged to be larger, there is provided a liquid electrostatic 圧直 kinematic guiding device, characterized in that.

  According to the present invention, by restricting the positional relationship between the concave portions formed on the plurality of bearing surfaces and the liquid supply holes formed on the bottom surfaces of the concave portions, the position around the center of gravity of the movable body when the movable body is moved is regulated. Moment fluctuation can be reduced. For this reason, the posture change at the time of movement of a movable body can be suppressed, without causing the enlargement and complication of an apparatus.

BRIEF DESCRIPTION OF THE DRAWINGS (a) based on the 1st Embodiment of this invention is a schematic structure sectional drawing of a hydrostatic pressure linear motion guide apparatus, (b) is a figure which shows the pressure distribution of each bearing clearance, (c) is each bearing The figure which shows typically the levitation force in a surface, and a levitation force action point. (A) When the movable body is stationary, (b) When the movable body is moved, the pressure distribution in the bearing gap (left figure) and that the pressure distribution is replaced by the levitation force and the levitation force action point, respectively. The figure shown (right figure). The partial cross section figure (upper figure) of a movable body for demonstrating the liquid supply point of a liquid hydrostatic bearing, and the center of a recessed part, and the top view (lower figure) which shows only a recessed part. The partial cross section figure (upper figure) of a movable body for demonstrating the liquid supply point in the case of having a some liquid supply hole, and the top view (lower figure) which shows only a recessed part. The cross section of the liquid hydrostatic bearing when the liquid supply point is arranged at the same position as the center of the recess, (b) at the front in the movement direction from the center, and (c) at the rear in the movement direction from the center. Fig. (Upper left), bearing gap pressure distribution (lower left), levitation force and levitation force action point (right). The schematic structure sectional drawing of the liquid static pressure linear motion guide apparatus which concerns on the 2nd Embodiment of this invention. The schematic structure sectional drawing of the liquid static pressure linear motion guide apparatus which concerns on the 3rd Embodiment of this invention. Schematic configuration perspective view of a hydrostatic bearing for explaining the relationship between the bearing surface (the oblique lattice region of (a)), the recess (the satin region of (b)) and the land (the lattice region of (b)) Figure. (A) is when the bearing surface is formed with a recess, (b) is when the bearing surface is not formed with a recess, and (c) is when the bearing surface is formed with a recess. FIG. 2 is a schematic sectional view (upper diagram) of a hydrostatic bearing, and a diagram (lower diagram) showing a pressure distribution in a bearing gap.

<First Embodiment>
A first embodiment of the present invention will be described with reference to FIGS. First, a schematic configuration of the liquid static pressure linear motion guide device will be described with reference to FIG.

[Liquid static pressure linear motion guide device]
As shown in FIG. 1A, the liquid static pressure linear motion guide device of the present embodiment includes a guide member 1a, a movable body 2, and a pressurized liquid supply device 9 as a liquid supply means. The guide member 1a is a rail-shaped member, for example, and has a guide surface 1 parallel to the moving direction of the movable body 2 on one side. The movable body 2 is, for example, a stage on which a workpiece of an ultra-precision processing machine is placed, and is movable along the guide member 1a in the arrow direction (left-right direction) in FIG. Is arranged. Examples of the driving mechanism include a ball screw mechanism. That is, a male screw is arranged in parallel with the guide member 1a, and this male screw is screwed into a female screw portion provided on the movable body 2 via a ball. And by driving a motor and rotating a male screw, the movable body 2 moves along a male screw based on the screwing of a male screw and a female screw part.

  In the case of the present embodiment, the support of the movable body 2 with respect to the guide member 1a is configured by a liquid hydrostatic bearing. For this purpose, the movable body 2 has a bearing surface 3 that constitutes a hydrostatic bearing with the guide surface 1, and is arranged in a state where a pressure is applied toward the guide surface 1. This pressure is applied by non-contact means such as a magnetic attraction force (or repulsive force) using a magnet or a fluid, and the bearing surface 3 of the movable body 2 is pressed against the guide surface 1. Act on. The pressurization is preferably applied almost uniformly in the entire moving direction of the movable body 2, and at least the moment is balanced around the center of gravity of the movable body 2.

  The liquid hydrostatic bearing forms a lubricating fluid film by forcibly supplying a pressurized fluid to the bearing gap 8 between the bearing surface 3 of the movable body 2 and the guide surface 1 of the guide member 1a. Then, the movable body 2 is floated in a non-contact manner by the balance between the pressure of the lubricating fluid film and the above-described pressure.

  The pressurized liquid supply device 9 supplies a liquid having a constant pressure between the bearing surface 3 and the guide surface 1 with, for example, a pump. In the case of the present embodiment, liquid is supplied between the bearing surface 3 and the guide surface 1 from the pressurized liquid supply device 9 via the fluid path 9 a of the movable body 2. Further, a throttle (not shown) is provided upstream of the fluid path 9a so that the pressure of the pressurized liquid sent from the pressurized liquid supply device 9 is once lowered and then sent to the fluid path 9a.

  In the case of the liquid static pressure linear motion guide device of the present embodiment configured as described above, the movable body 2 has a plurality of bearing surfaces 3 arranged in the moving direction of the movable body 2. In the case of the illustrated example, two are arranged in the movement direction, but three or more may be arranged, or they may be arranged in the front and back direction of the sheet of FIG. In any case, a plurality of bearing surfaces 3 are arranged side by side in at least the moving direction of the movable body 2.

  Each of the plurality of bearing surfaces 3 is formed with a recess 4 that opens toward the guide surface 1 and a liquid supply hole 7 that is disposed on the bottom surface 4a of the recess 4 and is supplied with liquid from the pressurized liquid supply device 9. ing. The liquid supply hole 7 may be formed on the wall surface of the recess 4. In the case of the present embodiment, the portion obtained by removing the opening surface 5 of the recess 4 from the bearing surface 3 is referred to as a land 6 as in the case described with reference to FIG. Therefore, the bearing surface 3 includes the opening surface 5 of the recess 4 and the land 6. The opening surface 5 of the recess 4 is included in the land 6.

  The liquid supply hole 7 formed in the recess 4 is connected to the fluid path 9 a, and the pressurized liquid supplied from the pressurized liquid supply device 9 passes through the liquid supply hole 7 and the recess 4 and the guide surface 1. It is supplied to a bearing gap 8 made up of lands 6. Then, a liquid hydrostatic bearing is formed as described above. In addition, the shape of the opening surface 5 of the bearing surface 3 and the recessed part 4 can be made into arbitrary shapes, such as a rectangle, circular, and an ellipse other than the square as shown in the above-mentioned FIG. Further, when the concave portion has such an arbitrary shape, the center is the geometric center of gravity of the shape. Further, the area of the bearing surface 3 and the area of the opening surface 5 of the recess 4 may be different or the same for each bearing surface 3. However, the moment around the center of gravity G of the movable body 2 is set to be balanced when the movable body 2 is stationary.

[Position of liquid supply hole]
Next, the position of the liquid supply hole 7 in each recess 4 will be described. When the movable body 2 is stationary, the bearing gap 8 of the liquid hydrostatic bearing having the recess 4 on the bearing surface 3 is generally shown in the left diagram of FIG. 2A regardless of the position of the liquid supply hole 7. A good pressure distribution. In this specification, the integrated value of the pressure distribution is referred to as a levitation force that is a force (a force acting in a direction opposite to the guide surface 1) that causes the movable body 2 acting on the bearing surface 3 to float.

  Further, as shown in the right diagram of FIG. 2A, the pressure distribution in the left diagram of FIG. 2A can be replaced equivalently by using the levitation force and its action point. Is called a levitation force action point Q in this specification. That is, when a plurality of cross sections parallel to the moving direction of the movable body 2 in the pressure distribution of the bearing gap 8 are taken in the direction perpendicular to the moving direction, the cross section with the average cross-sectional area is taken to have an area of 2 on both sides of the moving direction. The point on the line of action to be divided is called the levitation force action point Q. In the case of this embodiment, the shape of the bearing surface 3 is a square, and the shape of the space between the recess 4 and the opening surface 5 is a rectangular parallelepiped. For this reason, when a plurality of cross sections parallel to the moving direction of the movable body 2 in the pressure distribution of the bearing gap 8 are taken in the direction perpendicular to the moving direction, the cross sectional areas are almost the same. For this reason, the pressure distribution of an arbitrary cross section parallel to the moving direction of the movable body 2 in the bearing gap 8 becomes the pressure distribution shown in FIG. 2A, and a line that bisects the area of this pressure distribution on both sides of the moving direction. Becomes the action line, and the levitation force action point Q exists on this action line.

  As shown in FIG. 2A, the stationary pressure distribution of the movable body 2 is a target with respect to the center of the pressure distribution and is in a state balanced with respect to the moving direction of the movable body 2. That is, the levitation force action point Q is located at the center of the pressure distribution. On the other hand, when the liquid supply hole 7 is at the center of the movable body 2 of the recess 4, if the movable body 2 is moved in the left direction of FIG. 2, as illustrated in FIG. 2 (b) The pressure distribution becomes higher on the right side as shown in the left figure. Then, as shown in the right diagram of FIG. 2B, the levitation force action point Q moves to the right side of the case shown in FIG.

  As shown in FIG. 3, the geometric gravity center of the opening surface 5 of the recess 4 is referred to as the center N of the recess 4. The point where the center of the liquid supply hole 7 is projected perpendicularly to the opening surface 5 of the recess 4 is referred to as a liquid supply point P in the recess 4. Further, a plurality of liquid supply holes 7 may be provided in the recess 4 as shown in FIG. In this case, the liquid supply point P is the geometric center of gravity of the plurality of liquid supply holes 7 in the recess. When there is one liquid supply hole 7 for one recess 4, the center is the liquid supply point P as shown in FIG. 3. Hereinafter, the case where there is one liquid supply hole 7 for one recess 4 will be described as a representative, but when there are a plurality of liquid supply holes 7 for one recess 4, as described above. The geometric center of gravity can be handled similarly as the liquid supply point P.

  In the present embodiment, the plurality of liquid supply holes 7 are arranged so that the liquid supply point P satisfies the following conditions. That is, the sum of the distances in the movement direction between the liquid supply point P in each recess and the center of gravity G of the movable body 2 is the distance in the direction of movement between the center N of the recess and the center of gravity G of the movable body 2. Each liquid supply hole 7 is arranged so as to be larger than the total sum. In the case of this embodiment, a plurality of bearing surfaces 3, a plurality of recesses 4, and a plurality of liquid supply holes 7 are perpendicular to the moving direction of the movable body 2 and pass through the center of gravity G of the movable body 2. Are arranged symmetrically.

  Accordingly, each liquid supply hole 7 is arranged close to the outer end side of the movable body 2 from the center of the bottom surface of the recess 4 having itself. More specifically, with respect to the moving direction of the movable body 2, the separation distance Ls between the liquid supply point P and the center of gravity G of the movable body 2 is such that the center N of the recess 4 having the liquid supply point P itself and the center of gravity of the movable body 2. Each liquid supply hole 7 is arranged at a position larger than the separation distance Lp from G. A difference between the separation distance Ls and the separation distance Lp is defined as a separation distance D between the liquid supply point P and the center N of the recess 4.

  In terms of the positional relationship in FIG. 1A, the liquid supply point P is located on the left side of the center N of the concave portion 4 in the concave portion 4 of the liquid hydrostatic bearing located on the left side of the center of gravity G of the movable body 2. On the other hand, in the concave portion 4 of the liquid hydrostatic bearing on the right side of the center of gravity G of the movable body 2, the liquid supply point P is located on the right side of the center N of the concave portion 4.

[Moment fluctuation around the center of gravity when stationary and moving]
In the case of the present embodiment, when the movable body 2 moves to the left side in FIG. 1A with such a configuration, the liquid hydrostatic bearing on the left side in FIG. The pressure distribution in the bearing gap 8 is as shown in the left diagram of FIG. On the other hand, the pressure distribution in the bearing clearance 8 of the liquid hydrostatic bearing on the right side of FIG. 1A existing behind the moving direction of the movable body 2 is as shown on the right side of FIG. That is, the pressure distribution of the liquid hydrostatic bearing at the front in the moving direction is inclined so that the pressure increases as a whole as compared with the stationary state (broken line) and the pressure increases at the rear in the moving direction. On the other hand, the pressure distribution of the hydrostatic bearing at the rear in the moving direction is inclined such that the pressure is lower than that at rest (broken line) and the pressure is increased at the rear in the moving direction.

  As a result of such pressure distribution, as shown in FIG. 1 (c), the levitation force Fd1 of the liquid hydrostatic bearing in the forward direction of movement becomes larger than the levitation force Fs1 at rest, and the levitation force action point is Shift backward in the direction of movement than when stationary. On the other hand, the levitation force Fd2 of the liquid hydrostatic bearing at the rear in the movement direction is smaller than the levitation force Fs2 at rest, and the levitation force action point is shifted rearward in the movement direction than at rest.

  As a result, the moment around the center of gravity G of the movable body 2 by the liquid hydrostatic bearing forward in the moving direction during movement is shorter than the distance from the center of gravity compared to when stationary, but the acting force increases. On the other hand, the moment around the center of gravity G of the movable body 2 by the liquid hydrostatic bearing at the rear of the moving direction during movement is longer than the distance from the center of gravity compared to when stationary but the acting force is reduced. Therefore, the moment fluctuation around the center of gravity G of the movable body 2 when the movable body 2 moves can be reduced. For this reason, the posture change at the time of the movement of the movable body 2 can be suppressed, without causing the enlargement and complication of the apparatus.

  This point will be described in detail below. First, a configuration in which the liquid supply point P is arranged at the center N of the recess will be described as a comparative example, and the effects of the present embodiment will be described in comparison with this comparative example. The moment acting around the center of gravity G of the movable body 2 by the liquid hydrostatic bearing is expressed by the product of the levitation force by the liquid hydrostatic bearing and the distance between the levitation force action point and the center of gravity G of the movable body 2. The sum of moments around the center of gravity G of the movable body 2 by the liquid hydrostatic bearings is assumed to be balanced around the center of gravity G of the movable body 2 when the movable body 2 is stationary.

  In the case of the liquid hydrostatic linear motion guide device provided with the liquid hydrostatic bearing of the comparative example, when the movable body 2 moves, the levitation force action point moves rearward in the movement direction of the movable body 2. The moment fluctuates in the direction of lifting the direction rearward. However, in the present embodiment, the magnitude of the levitation force varies with the levitation force action point. The fluctuation of the levitation force is a direction in which the movable body 2 is lifted forward in the moving direction. Therefore, variation in the moment when the movable body 2 moves can be suppressed. Further details will be described.

  First, it will be described that the levitation force action point moves rearward in the moving direction of the movable body 2 regardless of the positional relationship between the liquid supply point P and the center N of the recess 4. When the movable body 2 moves, the concave portion 4 serves as a fluid pool, so that the flow rate restricted by the bearing gap 8 at the rear of the movable body 2 in the movement direction increases. On the other hand, the throttled flow rate is reduced in the bearing gap 8 in front of the movable body 2 in the moving direction. As a result, a pressure gradient that increases backward in the movement direction of the movable body 2 is generated. Since this occurs regardless of the position of the liquid supply point P, the levitation force action point moves backward in the movement direction of the movable body 2 regardless of the positional relationship between the liquid supply point P and the center N of the recess 4.

  Next, on the bearing surface 3 of the liquid hydrostatic bearing, when the movable body 2 moves, the pressure drop region in which the pressure drops from the supply pressure from the liquid supply hole 7 and the pressure rises from the supply pressure from the liquid supply hole 7. It will be explained that a pressure increase region occurs.

  In order to use the left figure of FIG. 5 (a) (b) (c), it demonstrates first. Each figure of FIG. 5 is a diagram showing the pressure distribution, levitation force, and levitation force action point in each case, assuming that the movable body 2 moves to the left side in the figure. In order to simplify the illustration, the pressure drop in the bearing gap 8 is approximated by a straight line. FIG. 5A shows a case where the liquid supply point P coincides with the center N of the recess 4. FIG. 5B shows a case where the liquid supply point P is located in front of the moving body 2 in the moving direction from the center N of the recess 4. FIG. 5C shows the case where the liquid supply point P is located behind the center N of the recess 4 in the moving direction of the movable body 2.

  As shown in the left diagrams of FIG. 5, the supply pressure Ps at the liquid supply point P is equal to the stationary state even when the movable body 2 is moved, so the pressure gradient in the recess 4 during the movement is the supply pressure at the liquid supply point P. Occurs based on Ps. Therefore, in the concave portion 4, the supply pressure Ps decreases from the liquid supply point P in the moving direction of the movable body 2, and increases from the liquid supply point P to the supply pressure Ps in the movement direction of the movable body 2. Due to this action, the pressure distribution on the bearing surface 3 includes a pressure drop region A1 in which the pressure decreases when stationary during movement, and a pressure increase region A2 where the pressure increases during stationary when compared with stationary.

  Next, it will be described that the ratio of the pressure drop region and the pressure rise region when the movable body 2 moves on the bearing surface 3 can be changed depending on the position of the liquid supply point P with respect to the center N of the recess 4. The boundary between the pressure drop region A1 and the pressure rise region A2 is a liquid supply point P. This is due to the following reason. That is, a liquid having a constant pressure is supplied from the liquid supply hole 7 into the recess 4 and flows toward the bearing gap 8. Therefore, in the moving direction ahead of the liquid supply point P, the direction in which the liquid flows from the liquid supply hole 7 is opposite to the moving direction. Then, the supplied flow rate tends to decrease, and the pressure decreases. On the other hand, behind the liquid supply point P, the direction in which the liquid flows from the liquid supply hole 7 is the same as the movement direction. Then, the supplied flow rate tends to increase, and the pressure increases.

  Accordingly, the moving direction front of the movable body 2 from the liquid supply point P is the pressure drop region A1, and the moving direction rear of the movable body 2 from the liquid supply point P is the pressure increase region A2. For this reason, by changing the position of the liquid supply point P with respect to the center N of the recess 4, the ratio of the pressure drop region A1 and the pressure rise region A2 on the bearing surface 3 when the movable body 2 is moved can be changed.

  Next, it will be described that the levitation force can be changed by changing the ratio of the pressure drop region A1 and the pressure rise region A2 on each bearing surface 3. As shown in the left figure of Fig.5 (a), when the liquid supply point P and the center N of the recessed part 4 correspond, the pressure fall area | region A1a and the pressure rise area | region A2a at the time of the movement of the movable body 2 are equal. For this reason, when the movable body 2 moves, the pressure integrated value F1a of the pressure decrease region A1a and the pressure integrated value F2a of the pressure increase region A2a become equal. As described above, since the integrated pressure value and the levitation force are equivalent, the levitation force does not change between when the movable body 2 is stationary and when it moves as shown in the right figure of FIG.

  However, as shown in the left diagram of FIG. 5B, when the liquid supply point P is located in front of the center N of the recess 4 in the moving direction of the movable body 2, the pressure increase area A2b during the movement of the movable body 2 is the pressure. It becomes larger than the lowered region A1b. For this reason, when the movable body 2 moves, the pressure integral value F2b of the pressure increase region A2b becomes larger than the pressure integral value F1b of the pressure decrease region A1b. Since the integrated pressure value and the levitation force are equivalent, the levitation force when the movable body 2 moves is larger than that when the movable body 2 is stationary, as shown in the right diagram of FIG.

  5C, when the liquid supply point P is located behind the center N of the recess 4 in the movement direction of the movable body 2, the pressure increase region A2c is reduced in pressure when the movable body 2 moves. It becomes smaller than area A1c. For this reason, when the movable body 2 moves, the pressure integrated value F2c of the pressure increasing region A2c becomes smaller than the pressure integrated value F1c of the pressure decreasing region A1c. Since the integrated pressure value and the levitation force are equivalent, the levitation force when the movable body 2 moves is smaller than that when the movable body 2 is stationary, as shown in the right diagram of FIG. As described above, it has been explained that the levitation force can be changed by changing the ratio between the pressure drop region A1 and the pressure rise region A2.

  Furthermore, in the liquid hydrostatic linear motion guide device of the present embodiment, it will be described that the moment acting on the movable body 2 can be suppressed by changing the levitation force on the bearing surface 3 of each liquid hydrostatic bearing. In the present embodiment, the hydrostatic bearing shown in FIG. 1 (a) in front of the movable body 2 in the moving direction from the center of gravity G of the movable body 2 takes the form shown in FIG. The hydrostatic bearing behind the center of gravity G of the movable body 2 in the moving direction takes the form shown in FIG. In the following description, the movable body 2 is assumed to move to the left in each drawing, and the positional relationship is related to the moving direction of the movable body 2 and will be described using the positional relationship in each drawing.

First, the liquid hydrostatic bearing provided on the left side of the center of gravity G of the movable body 2 will be described. As shown in FIG. 1C, when the movable body 2 is stationary, the levitation force is Fs1, and the distance between the levitation force action point Qs1 and the center of gravity G of the movable body 2 is Xs1. Further, when the movable body 2 moves, the levitation force is Fd1, and the distance between the levitation force action point Qd1 and the center of gravity G of the movable body 2 is Xd1. The difference between Fs1 and Fd1 is ΔF1, and the difference between Xs1 and Xd1 is ΔX1. When the movable body 2 is stationary, the moment Ms1 around the center of gravity G of the movable body 2 that lifts the left side of the movable body 2 is:
Ms1 = Fs1 × Xs1 (1)
It is represented by

Here, the case where the liquid hydrostatic bearing of the comparative example as shown in FIG. 5A is applied to the structure of FIG. 1 is considered. In the case of the comparative example, the floating force when the movable body 2 is stationary is equal to the floating force when the movable body 2 is moved. Since the levitation force at rest is constant regardless of the position of the liquid supply point P, this levitation force is Fs1. Therefore, in the case of the comparative example, when the movable body 2 moves, the moment Mdp1 around the center of gravity G of the movable body 2 that lifts the left side of the movable body 2 is
Mdp1 = Fs1 × (Xs1−ΔX1) (2)
It is represented by

On the other hand, in the structure of this embodiment, in the liquid hydrostatic bearing provided on the left side of the center of gravity G of the movable body 2, the levitation force increases when the movable body 2 moves, so Fd1 = Fs1 + ΔF1. Therefore, when the movable body 2 moves, the moment Md1 around the center of gravity G of the movable body 2 that lifts the left side of the movable body 2 is
Md1 = (Fs1 + ΔF1) × (Xs1−ΔX1) (3)
It is represented by

  As can be seen from the comparison between the formula (1) and the formula (2), in the liquid hydrostatic linear motion guide device having the liquid hydrostatic bearing of the comparative example, the levitation force is the same when stationary and when moving. On the other hand, the distance between the levitation force action point and the center of gravity G of the movable body 2 is smaller when moving than when stationary. For this reason, at the time of movement, the moment Mdp1 for lifting the left side of the movable body 2 becomes small.

  On the other hand, in this embodiment, as can be seen by comparing the equations (1) and (3), the distance between the point of action of the levitation force and the center of gravity G of the movable body 2 becomes smaller when moving relative to the stationary state. The levitation force itself increases. For this reason, the fluctuation | variation of a moment can be suppressed at the time of stationary and a movement.

Next, the liquid hydrostatic bearing provided on the right side of the center of gravity G of the movable body 2 will be described. As shown in FIG. 1C, when the movable body 2 is stationary, the levitation force is Fs2, and the distance between the levitation force action point Qs2 and the center of gravity G of the movable body 2 is Xs2. Further, when the movable body 2 moves, the levitation force is Fd2, and the distance between the levitation force action point Qd2 and the center of gravity G of the movable body 2 is Xd2. The difference between Fs2 and Fd2 is ΔF2, and the difference between Xs2 and Xd2 is ΔX2. When the movable body 2 is stationary, a moment Ms2 around the center of gravity of the movable body that lifts the right side of the movable body 2 is:
Ms2 = Fs2 × Xs2 (4)
It is represented by

Here, the case where the liquid hydrostatic bearing of the comparative example as shown in FIG. 5A is applied to the structure of FIG. 1 is considered. In the case of the comparative example, the floating force when the movable body 2 is stationary is equal to the floating force when the movable body 2 is moved. Since the levitation force at rest is constant regardless of the position of the liquid supply point P, this levitation force is Fs2. Therefore, in the case of the comparative example, when the movable body 2 moves, the moment Mdp2 around the center of gravity G of the movable body 2 that lifts the right side of the movable body 2 is
Mdp2 = Fs2 × (Xs2 + ΔX2) (5)
It is represented by

On the other hand, in the structure of the present embodiment, in the hydrostatic bearing provided on the right side of the center of gravity G of the movable body 2, the levitation force decreases when the movable body 2 moves, so Fd2 = Fs2-ΔF2. Therefore, when the movable body 2 moves, the moment Md2 around the center of gravity G of the movable body 2 that lifts the right side of the movable body 2 is
Md2 = (Fs2−ΔF2) × (Xs2 + ΔX2) (6)
It is represented by

  As can be seen from the comparison between Equation (4) and Equation (5), the liquid hydrostatic linear motion guide device having the liquid hydrostatic bearing of the comparative example has the same levitation force when stationary and when moving. On the other hand, the distance between the point of action of the levitation force and the center of gravity G of the movable body 2 is greater when moving than when stationary. For this reason, during movement, the moment Mdp2 for lifting the right side of the movable body 2 increases.

  On the other hand, in this embodiment, as can be seen by comparing the equations (4) and (6), the distance between the levitation force action point and the center of gravity G of the movable body 2 is increased when moving relative to the stationary state, The levitation force itself is reduced. For this reason, the fluctuation | variation of a moment can be suppressed at the time of stationary and a movement. As a result, it is possible to suppress the posture change during the movement of the movable body 2 without increasing the size and complexity of the apparatus.

  As described above, when the movable body 2 is moved, the levitation force action point of each liquid hydrostatic bearing moves. However, the levitation force of each liquid hydrostatic bearing can be changed depending on the position of the liquid supply point P. The effect that the fluctuation of the moment acting on the movable body 2 can be suppressed has been described.

  Further, the movement of the plurality of liquid supply points P is performed by adding the condition that the liquid supply holes 7 are arranged at positions symmetrical with respect to a virtual plane M that passes through the center of gravity G of the movable body 2 and is perpendicular to the movement direction. The inclination of the movable body 2 at the time can be suppressed. This is because the levitation force ΔF1 increasing on the left side of the center of gravity G of the movable body 2 in FIG. 1A and the levitation force ΔF2 decreasing on the right side in FIG. This is because the sum of forces can be made the same. In this case, the plurality of bearing surfaces 3 and the plurality of recesses 4 are also symmetric about the virtual plane M. In this case, even if the moving direction of the movable body 2 is opposite to the above-described case, the same action as described above can be obtained.

  Further, the number of bearing surfaces 3 in the moving direction may be three or more in addition to two as shown in FIG. However, as described above, the position of the liquid supply point P on each bearing surface 3 is set in consideration of the moment around the center of gravity G of the movable body 2 during movement. In addition, the position of the liquid supply point P on each bearing surface 3 is preferably set so that the moments around the center of gravity G of the movable body 2 during movement are balanced, not limited to the number of the bearing surfaces 3.

[Example]
The result of the numerical analysis performed in order to confirm the effect of this embodiment mentioned above is demonstrated. Here, the movable body 2 has the structure shown in FIG. 1A, the bearing surface 3 is 50 × 50 mm, the distance between the bearings is 50 mm, and the tilt angle of the movable body 2 at that time was obtained. Note that the distance in the moving direction between the center N of the recess 4 and the liquid supply point P is D. The inter-bearing distance is the distance between the end portions of the bearing surfaces 3 adjacent to each other in the moving direction that face each other.

  From the numerical analysis results shown in Table 1, it can be seen that the sign of the tilt angle changes when the distance D in the moving direction of the center N of the recess 4 and the liquid supply point P is between 10 mm and 11 mm. Therefore, under the conditions of the present embodiment, the position of the liquid supply point P in each concave portion 4 is 10 mm to 11 mm apart from the center N of the concave portion 4 in the direction away from the center of gravity G of the movable body 2 in the moving direction of the movable body 2. It is good to arrange with the distance D. In this case, the posture change occurring in the movable body 2 can be made extremely small. The separation distance D needs to be changed according to changes in conditions such as supply pressure, liquid hydrostatic bearing arrangement, and bearing clearance.

<Second Embodiment>
A second embodiment of the present invention will be described with reference to FIG. In the case of the present embodiment, the position of the liquid supply point P is slightly shifted forward in the movement direction from the center N of the recess 4 in the liquid hydrostatic bearing at the rear of the movable body 2 in the movement direction (right side in FIG. 6). In the liquid hydrostatic bearing in front of the movable body 2 in the moving direction (left side in FIG. 6), the position of the liquid supply point P is larger in the moving direction forward than the center N of the recess 4 and larger than in the liquid hydrostatic bearing in the rearward moving direction. It is shifted. Then, with respect to the moving direction of the movable body 2, the sum (Ls1 + Ls2) of the separation distance between each liquid supply point P and the center of gravity G of the movable body 2 is the center N of the recess 4 having the liquid supply point P itself and the movable body 2. Is larger than the sum (Lp1 + Lp2) of the separation distance from the center of gravity G.

  In this case, both liquid hydrostatic bearings are in the form shown in FIG. 6B, and the levitation force increases in both. However, since the amount of shift from the center N is larger in the forward direction of movement, the levitation force is also increased. For this reason, the fluctuation | variation of the moment around the gravity center G of the movable body 2 can be suppressed as a whole. Other structures and operations are the same as those in the first embodiment.

<Third Embodiment>
A third embodiment of the present invention will be described with reference to FIG. In the present embodiment, a plurality of liquid supply holes 7 are provided in the recess 4. In this case, the geometric gravity center point of the plurality of liquid supply holes 7 in the same recess is handled as the liquid supply point P as described with reference to FIG. The positions of the plurality of liquid supply holes 7 in the recess 4 are set so that the liquid supply point P is shifted from the center N of the recess 4 to the outer end side of the movable body 2.

  Also in this embodiment, the sum of the distances in the moving direction between the liquid supply point P and the center of gravity G of the movable body 2 is calculated as the center N of the recess 4 having the liquid supply point P itself and the center of gravity G of the movable body 2. The sum of the distances between the movable body 2 and the momentum G around the center of gravity G can be suppressed. Other structures and operations are the same as those in the first embodiment.

<Other embodiments>
The above-described embodiments can be implemented in combination as appropriate. Further, even if the position of the liquid supply point P on any bearing surface coincides with the center N of the recess 4, the position of the liquid supply point P is shifted from the center N of the recess 4 on the other bearing surface to supply the liquid. The sum of the distances between the point P and the center of gravity G is made larger than the sum of the distances between the center N and the center of gravity G. Thereby, the fluctuation | variation of the moment of the movable body 2 as mentioned above can be suppressed.

  DESCRIPTION OF SYMBOLS 1 ... Guide surface, 1a ... Guide member, 2 ... Movable body, 3 ... Bearing surface, 4 ... Recessed part, 4a ... Bottom surface, 5 ... Opening surface, 6 ... Land, 7 ... Liquid supply hole, 8 ... Bearing gap, 9 ... Pressurized liquid supply device, G ... Center of gravity (of movable body), N ... Center of recess (recessed), P ... liquid supply point, Q ... levitation force acting point, Lp ... distance in the moving direction of the movable body between the center of the recess and the center of gravity of the movable body, Ls ... liquid supply point and movable body Distance in the moving direction of the movable body from the center of gravity

Claims (2)

A guide member having a guide surface;
A movable body that has a bearing surface that constitutes a hydrostatic bearing with the guide surface, is arranged in a state where a pressurized pressure is applied toward the guide surface, and moves along the guide member;
In a liquid static pressure linear motion guide device comprising: a liquid supply means for supplying a liquid between the bearing surface and the guide surface;
The movable body is arranged by arranging a plurality of the bearing surfaces in the moving direction,
Each of the plurality of bearing surfaces is formed with a recess that opens toward the guide surface, and a liquid supply hole that is disposed on the bottom surface or wall surface of the recess and is supplied with liquid from the liquid supply means.
The plurality of liquid supply holes have a total sum of distances in the moving direction between a liquid supply point that is a geometric center of gravity of the liquid supply hole in each recess and a center of gravity of the movable body. It is arranged to be larger than the sum of the distances in the moving direction between the center and the center of gravity of the movable body,
A hydrostatic linear motion guide device characterized by the above. The plurality of bearing surfaces, the plurality of recesses, and the plurality of liquid supply points are arranged symmetrically with respect to a virtual plane that is perpendicular to the moving direction of the movable body and passes through the center of gravity of the movable body.
The liquid static pressure linear motion guide device according to claim 1, wherein

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