Hydrostatic bearing device and machine tool main spindle device with hydrostatic bearing device

Abstract

Hydrostatic bearing device with: a rotating wave (131); and a bearing metal (14) with a hydrostatic section (18) which allows the rotating shaft (131) to be rotatably supported, wherein the hydrostatic section (18) comprises a bearing clearance (20) located between a surface of the rotating shaft (131) and the bearing metal (14) and filled with a lubricating solution (R), a bearing surface section (22) facing the surface of the rotating shaft (131), a plurality of pockets (24) recessed side by side in a circumferential direction of the bearing surface section (22), and web sections (30) each projecting from a bottom section (26) of a corresponding pocket (24) towards the surface of the rotating shaft (131) and having an end face (32) facing the surface of the rotating shaft (131) and a groove section (40) located between the web section (30) and an edge (28) of the pocket (24). the groove section (40) side groove sections (42) which are located on both sides of each web section (30) such that they extend in the circumferential direction, have an upstream groove section (44) which is positioned upstream in a rotational direction of the rotating shaft (131), and a downstream groove section (46) which is positioned downstream in the rotational direction, the groove section (40) has a supply path (16) that communicates with the upstream groove section (44) to supply the hydrostatic section (18) with the lubricating solution (R), the bearing clearance (20) has a first bearing clearance (C) between the surface of the rotating shaft (131) and the bearing surface section (22) and a second bearing clearance (H) between the surface of the rotating shaft (131) and the end face (32), the size of the second storage game (H) is designed to be larger than the size of the first storage game (C), when the density of the lubricating solution (R) is denoted by ρ, a viscosity coefficient of the lubricating solution (R) is denoted by µ, a circumferential speed of the rotating shaft (131) is denoted by U and the size of the second bearing play (H) is denoted by H, a Reynolds number for the second bearing clearance (H) is expressed by Re = ρUH / µ and for a flow of the lubricating solution (R) that takes place through the second bearing clearance (H) when the rotating shaft (131) is rotatably supported, Re < 2000 applies.

Description

BACKGROUND OF THE INVENTION 1. Field of the invention

[0001] The invention relates to a hydrostatic bearing device and a machine tool main spindle device with a hydrostatic bearing device. 2. State of the art

[0002] Hydrostatic bearing devices are known from JP 2001 - 304 260 A, JP S57 - 107 426 A, US 4 307 918 A and DE 24 09 036 B2, in which a rotating shaft, such as a main spindle of a machine tool, which rotates at high speed, is supported by the hydrostatic pressure of a pressurized fluid, such as a lubricating solution.

[0003] JP 2001-304260A discloses a technique for a hydrostatic bearing device comprising a bearing metal with a hydrostatic section that supports the rotating shaft in such a way that the rotating shaft is rotatable. According to this technique, the hydrostatic section has a bearing surface section with a bearing clearance between the bearing surface section and a surface of the rotating shaft, and a plurality of pockets recessed adjacent to one another in a circumferential direction within the bearing surface section. A fluid, such as a lubricating solution, is fed into the pockets to support the rotating shaft by means of fluid pressure (static pressure).

[0004] As in Fig. 9 and Fig. As shown in Figure 10, the lubricating solution used for the hydrostatic bearing assembly is subject to a flow resulting from the rotation of the rotating shaft, a phenomenon known as pocket entrainment. The lubricating solution forms a flow in one direction of rotation of the rotating shaft and a flow in the opposite direction to the rotation of the rotating shaft, which occurs at the bottom of each pocket. Consequently, a large velocity gradient can develop in the hydrostatic bearing assembly near the surface of the rotating shaft, and high fluid shear resistance can result in energy loss. Within the pocket, a highly turbulent flow occurs with a Reynolds number of 20,000 to 30.000, and thus a large velocity gradient can form near the surface of the rotating shaft, and energy loss can result from high fluid shear resistance. This tendency becomes more pronounced when the rotating shaft rotates at high speed. BRIEF SUMMARY OF THE INVENTION

[0005] One object of the invention is to suppress a possible increase in the velocity gradient of a fluid in pockets in a hydrostatic bearing device in order to reduce energy loss.

[0006] A hydrostatic bearing device according to the invention has the features of claim 1.

[0007] In the hydrostatic bearing device according to the invention, the hydrostatic section has web sections, each projecting from the bottom section of the corresponding pocket towards the surface of the rotating shaft. These web sections have an end face facing the surface of the rotating shaft and a groove section located between the web section and the edge of the pocket. The groove section has side groove sections located circumferentially on both sides of each web section, an upstream groove section positioned upstream in the direction of rotation of the rotating shaft, and a downstream groove section positioned downstream in the direction of rotation. The groove section has a supply path that communicates with the upstream groove section to supply the hydrostatic section with the lubricating solution.Consequently, the lubricating solution flows in the direction of rotation of the rotating shaft across the end face and in the side groove sections in a direction opposite to the rotation of the rotating shaft. This makes it less likely that the flow across the end face and the flow in the side groove sections will interfere with each other. Thus, a potential increase in the fluid velocity gradient in the pockets of the hydrostatic bearing device is suppressed, which reduces energy loss.If the density of the lubricating solution is denoted by p, the viscosity coefficient of the lubricating solution by µ, the circumferential speed of the rotating shaft by U, and the size of the second bearing clearance by H, then the Reynolds number for the second bearing clearance is expressed by Re = ρ UH / µ. For the flow of the lubricating solution through the second bearing clearance when the rotating shaft is rotatably supported, Re < 2000. This means that, in conjunction with the flow of the lubricating solution through the second bearing clearance, a high fluid shear resistance is less likely to occur, thus suppressing energy loss.

[0008] In the hydrostatic bearing device according to the invention, the lubricating solution can be water or an aqueous solution in which 90% or more of its composition is water, or a low-viscosity mineral oil.

[0009] In the hydrostatic bearing device according to the invention, the lubricating solution flowing through the second bearing clearance when the rotating shaft is rotatably supported can form a laminar flow along the direction of rotation of the rotating shaft, and part of the laminar flow of the lubricating solution can move via the side groove sections to the upstream groove section with the supply path.

[0010] In the hydrostatic bearing device according to the invention, the lubricating solution flowing through the second bearing clearance forms a laminar flow along the direction of rotation of the rotating shaft, and a portion of this laminar flow moves via the side groove sections to the upstream groove section containing the supply path. Consequently, the web sections separate the laminar flow through the second bearing clearance from the flow in the side groove sections in the opposite direction to the direction of rotation. This makes it less likely that the laminar flow and the flow in the opposite direction of rotation will interfere with each other. Therefore, a potential increase in the velocity gradient of the fluid in the pocket is suppressed, which further reduces energy loss.

[0011] The hydrostatic bearing device according to the invention can be used to design a machine tool main spindle device that supports a machine tool main spindle in such a way that the machine tool main spindle is rotatable. In this way, the hydrostatic bearing device described above is used suitablely for the machine tool main spindle device. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] The above and further features and advantages of the invention will become apparent with reference to the accompanying drawings, in which the same numbers are used to represent the same elements, by means of the following description of exemplary embodiments. They show: Fig. 1 a top view showing a general design of a grinding machine, which is taken as an example of a machine tool main spindle device containing a hydrostatic bearing device according to an embodiment; Fig. 2 a right side view of the in Fig. 1 grinding machine shown; Fig. 3 an enlarged sectional view of section III in Fig. 1; Fig. 4 a sectional view along line IV-IV in Fig. 3; Fig. 5 a perspective view showing the bearing metal partially removed to reveal its internal shape; Fig. 6 an enlarged sectional view along line IV-IV in Fig. 3, representing a flow of a lubricating solution in a pocket; Fig. 7 a velocity distribution diagram for the flow of the lubricating solution in the pocket; Fig. 8 a diagram illustrating the energy consumption of the hydrostatic bearing device; Fig. 9 a velocity distribution diagram for a flow of a lubricating solution in a conventional pocket; and Fig. 10 a diagram illustrating the flow of a lubricating solution in the conventional pocket. DETAILED DESCRIPTION OF EXAMPLES OF EXECUTION

[0013] Using the drawings, a hydrostatic bearing device and a machine tool main spindle device with a hydrostatic bearing device are described below as an embodiment in which the invention is realized.

[0014] Fig. Figure 1 is a top view showing a general design of a grinding machine 10 as an example of a machine tool main spindle device with a hydrostatic bearing device according to an embodiment. Fig. Figure 2 is a right-side view of the grinding machine 10. Fig. Figure 2 omits the representation of a workpiece holding device 150 with a holding table 151. In all drawings depicting an X-axis, a Y-axis, and a Z-axis, the X-axis, Y-axis, and Z-axis are perpendicular to each other, with the Y-axis representing a vertical upward direction and the Z-axis and X-axis representing a horizontal direction. The Z-axis direction is parallel to a grinding wheel rotation axis L1 (in other words, a workpiece rotation axis direction). The X-axis direction is perpendicular to the grinding wheel rotation axis L1, and in this direction, a grinding wheel 132 cuts a workpiece W. The grinding wheel rotation axis L1, a workpiece rotation axis L2, and a dressing rotation axis L3 are all parallel to the Z-axis direction.

[0015] The in Fig. 1 and Fig. The grinding machine 10 shown in Figure 2 is designed to grind the workpiece W by moving the grinding wheel 132 relative to the workpiece W in the X-axis and Z-axis directions. A Z-axis sliding table 112 is located in a central section on a flat, rectangularly shaped column 110. This table slides along a pair of Z-axis guide rails 111 extending in the Z-axis direction. The Z-axis sliding table 112 is moved in the Z-axis direction by the rotation of a Z-axis feed spindle 113, which is driven by a Z-axis drive motor 114. The drive motor is operatively controlled by a control device 180 (NC control device or the like).The Z-axis drive motor 114 is equipped with a Z-axis direction position sensing device 115, such as an encoder, which detects the rotation angle of a drive shaft of the Z-axis drive motor 114 and sends a corresponding detection signal to the control device 180 to determine the position of the Z-axis direction sliding table 112 in the Z-axis direction. The control device 180 can move the grinding wheel 132 in the Z-axis direction using the Z-axis drive motor 114 relative to the dresser 177 or the workpiece W in order to detect, based on the detection signal from the Z-axis direction position sensing device 115, a movement path of the grinding wheel 132 in the Z-axis direction relative to the dresser 177 or the workpiece W.

[0016] On the Z-axis sliding table 112 is an X-axis sliding table 122, which slides along a pair of X-axis guide rails 121 running in the X-axis direction. The X-axis sliding table 122 is moved in the X-axis direction by a rotation of an X-axis feed spindle 123, which is actuated using an X-axis drive motor 124 as a drive source and is operationally controlled by the control device 180. The X-axis drive motor 124 is equipped with an X-axis direction position detection device 125 such as an encoder, which detects a rotation angle of a drive shaft of the X-axis drive motor 124 and sends a corresponding detection signal to the control device 180 to determine the position of the X-axis direction sliding table 122 in the X-axis direction.The control device 180 can move the grinding wheel 132 in the X-axis direction relative to the dresser 177 and the workpiece W using the X-axis drive motor 124, in order to detect the movement path of the grinding wheel 132 in the X-axis direction relative to the dresser 177 or the workpiece W based on the detection signal from the X-axis direction position detection device 125.

[0017] On the X-axis sliding table 122, a grinding wheel drive motor 126 and a grinding wheel shaft holder 130 are located. A pulley 127 is provided above a drive shaft of the grinding wheel drive motor 126. A pulley 128 is provided along the axis of a grinding wheel shaft 131 (a grinding wheel shaft that rotates about the grinding wheel rotation axis L1, which is parallel to the Z-axis). The grinding wheel shaft 131 is provided with the generally cylindrical grinding wheel 132 at its other end along its axis. A belt 129 forms a loop between the pulley 127 and the pulley 128 to transmit torque from the drive shaft of the grinding wheel drive motor 126 to the grinding wheel shaft 131 via the belt 129.

[0018] On the stand 110, a workpiece holding device 140 and a workpiece holding device 150 are located on the workpiece rotation axis L2, which is parallel to the Z-axis direction. The workpiece holding devices 140 and 150 hold the shaft-like workpiece W in a set position while rotating the workpiece W around the workpiece rotation axis L2, which runs in the Z-axis direction. The workpiece holding device 140 has a holding table 141 attached to the stand 110, a holding shaft housing 142 that can move back and forth on the workpiece rotation axis L2 relative to the holding table 141, and a holding shaft component 143 that is supported in the holding shaft housing 142 in such a way that it can rotate around the workpiece rotation axis L2. A central component 144 is provided at the tip of the holding shaft component 143, which carries a central section of an end face of the workpiece W.The holding shaft component 143 is rotated to any desired angle at any angular velocity using a holding shaft motor as a drive source (not shown in the drawings), which is operationally controlled by the control device 180. Like the workpiece holding device 140, the workpiece holding device 150 has a holding table 151, a holding shaft housing 152, a holding shaft component 153, and a central component 154. The holding shaft housing 142 is provided with a dressing device 160, which has a dresser 177 that is mounted so that it can be rotated about a dresser rotation axis L3. As shown in... Fig. As shown in Figure 2, the grinding wheel rotation axis L1, the workpiece rotation axis L2 and the dresser rotation axis L3 are all located on an imaginary plane VM, which is a plane parallel to the X-axis and Z-axis directions.

[0019] As described above, the grinding machine 10 moves the grinding wheel 132 relative to the workpiece W or the dresser 177 in the Z-axis direction and X-axis direction to grind the workpiece W or to externally reshape the grinding wheel 132 using the dresser 177.

[0020] Fig. 3 is an enlarged sectional view (a section III in Fig. 1) of the grinding wheel shaft holder 130. Fig. 4 is a sectional view along line IV-IV in Fig. 3. Fig. Figure 5 is a perspective view showing the bearing metal, which has been partially cut out to reveal its internal shape. Fig. Figure 6 is an enlarged sectional view along line IV-IV in Fig. 3 and represents a flow of a lubricating solution in a pocket. As in Fig. As shown in Figure 3, the grinding wheel shaft holder 130 has a grinding wheel shaft housing 12 and a bearing metal 14, which is fixed in the grinding wheel shaft housing 12. The grinding wheel shaft 131 (rotating shaft) is rotatably supported by the bearing metal 14. As shown in Fig. As shown in Figure 4, the bearing metal 14 has a hydrostatic section 18 which allows the grinding wheel shaft 131 to operate with fluid pressure (static pressure) of a fluid, such as a lubricating solution R, supplied by a pump P (see Figure 4). Fig. 4) or the like, is fed into the bearing metal 14 via a channel 16, to be rotatably supported. The bearing metal 14 is, as in Fig. Figure 5 is designed as a steel tube. The hydrostatic section 18 has a bearing clearance 20, a bearing surface section 22, a plurality of pockets 24 and web sections 30, which, as shown in Figure 5, are ... are designed as shown in Figure 5. Fig. As shown in Figure 6, all components are formed on an inner circumferential surface of the bearing metal 14. The lubricating solution R is preferably water or an aqueous solution in which 90% or more of its composition is water, or low-viscosity mineral oil.

[0021] The bearing surface section 22 is a surface which, as in Fig. 5 and Fig. Figure 6 shows a surface of the grinding wheel shaft 131. The pockets 24 are areas in which the lubricating solution R, supplied by the pump P or the like via the channel 16, is stored. The plurality of separate pockets 24 are recessed side by side in a circumferential direction in the bearing surface section 22 of the bearing metal 14. In this embodiment, the lubricating solution R is supplied via the channel 16 into each of four pockets 24. The number of pockets 24 is not limited to four. The fluid that flows out of the pockets 24 and axial pockets (not shown in the drawings) after being used for the hydrostatic support of the grinding wheel shaft 131 in the pockets is collected via a drain (not shown in the drawings), cooled by an oil cooler or the like, and then returned to a container T (see Figure 6). Fig. 4).

[0022] Each web section 30 projects from a bottom section 26 of the pocket 24 to a surface of the grinding wheel shaft 131 and has an end face 32 facing the surface of the grinding wheel shaft 131 and a groove section 40 located between the web section 30 and an edge 28 in the pocket 24. The groove section 40 has side groove sections 42 located on both sides of the web section 30 such that they extend circumferentially, an upstream groove section 44 positioned upstream in the direction of rotation of the rotating shaft, and a downstream groove section 46 positioned downstream in the direction of rotation. The groove section 40 also has a channel 16 (supply path) that communicates with the upstream groove section 44 to supply the hydrostatic section 18 with the lubricating solution R.

[0023] The bearing clearance 20 is a space located between the surface of the grinding wheel shaft 131 and the bearing metal 14, and is filled with the lubricating solution R. The bearing clearance 20 has a first bearing clearance C between the surface of the grinding wheel shaft 131 and the bearing surface section 22, and a second bearing clearance H between the surface of the grinding wheel shaft 131 and the end face 32. The size of the second bearing clearance H is set larger than the size of the first bearing clearance C. The inner circumferential surface of the bearing metal 14 is machined to form the multiple pockets 24 and the web sections 30 in the pockets 24.Thus, the hydrostatic section 18 in the bearing metal 14 has the bearing clearance 20, which lies between the surface of the grinding wheel shaft 131 and the bearing metal 14 and is filled with the lubricating solution R, the bearing surface section 22, which faces the surface of the grinding wheel shaft 131, the plurality of pockets 24, which are recessed in the bearing surface section 22 and lie side by side in the circumferential direction of the bearing surface section 22, and the web sections 30, which each project from the bottom section 26 of the corresponding pocket 24 to the surface of the grinding wheel shaft 131 and which have the end face 32, which faces the surface of the grinding wheel shaft 131, and the groove section 40, which lies between the web section 30 and the edge 28 of the pocket 24.

[0024] The grinding wheel shaft 131 is supported by the fluid pressure (static pressure) of a fluid, such as the lubricating solution R, which is fed into the pockets 24. If, in this context, the density of the lubricating solution R is denoted by p, the viscosity coefficient of the lubricating solution R is denoted by µ, the circumferential speed of the grinding wheel shaft 131 is denoted by U, and the size of the second bearing clearance is denoted by H, then a Reynolds number Re for the second bearing clearance H is expressed by Re = ρUH / µ. The circumferential speed U of the grinding wheel shaft 131 is set, for example, based on a design standard specification speed for the grinding wheel shaft 131, an estimated commonly used rotational speed and average speed, a specification speed based on machining conditions, and the like.The size of the second bearing clearance H is adjusted such that the flow rate of the lubricating solution R, which occurs when the grinding wheel shaft 131 is rotatably supported, is Re < 2000. The lubricating solution R flowing through the second bearing clearance H when the grinding wheel shaft 131 is rotatably supported forms a laminar flow along the direction of rotation of the grinding wheel shaft 131. Part of the laminar flow of the lubricating solution R is blocked by the edge 28 of the pocket 24 and moves via the downstream groove section 46 and the side groove sections 42 to the upstream groove section 44 with the channel 16. Thus, the lubricating solution R flowing through the side groove sections 42 flows in a direction opposite to the direction of rotation of the grinding wheel shaft 131.

[0025] As in the Fig. 9 and Fig. As shown in Figure 10, the lubricating solution R in a conventional pocket 224, which does not have the web section 30, is subject to a flow resulting from the rotation of a grinding wheel shaft 231, which is called carry-along in the pocket 224. The lubricating solution R forms a flow in the direction of rotation of the grinding wheel shaft 231 and a flow in a direction opposite to the direction of rotation of the grinding wheel shaft 231, which occurs near the bottom section 226 of the pocket 224. Accordingly, a large velocity gradient can form in the hydrostatic bearing device near the surface of the grinding wheel shaft 231, and energy loss can result from high fluid shear resistance. In a situation where the lubricating solution R in the bearing exhibits a highly turbulent flow with a Reynolds number of 20,000 to 30,The velocity gradient of the flow of the lubricating solution R is expressed by ∂S / ∂K, where the depth of the pocket is denoted by K and the circumferential speed of the grinding wheel shaft 231 is denoted by S. In this respect, for the viscosity coefficient µ of the lubricating solution R, a shear force τ1 exerted on the grinding wheel shaft 231 is expressed by τ1 = µ × (∂S / ∂K). If the opening area of ​​the pocket 224 is denoted by A, an energy loss P1 imposed on the grinding wheel shaft 231 by the lubricating solution R in the pocket 224 is expressed by P1 = S × τ1 × A. Since the circumferential speed S of the grinding wheel shaft 231 and the opening area A of the pocket 224 have fixed values, the shear force τ1 contributes to the energy loss P1. If changes in the temperature of the lubricating solution R are constant, the viscosity coefficient µ is constant.Consequently, the velocity gradient ∂S / ∂K at τ1 is a factor that contributes to the energy loss P1.

[0026] In a situation where the lubricating solution R is in the bearing, as in Fig. Since the flow is laminar, as shown in Figure 6, the velocity gradient can be approximated by U / H. A shear force τ2 exerted on the grinding wheel shaft 131 is expressed by τ2 = µ × (U / H). If the opening area of ​​the pocket 24 is denoted by A, an energy loss P2 imposed on the grinding wheel shaft 131 by the lubricating solution R in the pocket 24 is expressed by P2 = U × τ2 × A. Since the circumferential velocity U of the grinding wheel shaft 131 and the opening area A of the pocket 24 have fixed values, the shear force τ2 contributes to the energy loss P2. If changes in the temperature of the lubricating solution R are constant, the viscosity coefficient µ is constant. Consequently, τ2 is a factor that causes the H of the velocity gradient U / H to contribute to the energy loss P2.

[0027] Thus, in this embodiment, the web sections 30 are used for the hydrostatic section 18 to create a laminar flow near the surface of the grinding wheel shaft 131, while, as in the Fig. 6 and Fig. As shown in Figure 7, the laminar flow is separated into the flow in the direction of rotation of the grinding wheel shaft 131 and the flow through the side groove sections 42 in the pocket 24 in the opposite direction to the direction of rotation of the grinding wheel shaft 131, thus preventing the flows from interfering with each other. The magnitude of the second bearing clearance H between the end face 32 of each web section 30 and the surface of the grinding wheel shaft 131 is set to a maximum value to the extent that the laminar flow can be maintained. Due to this design of the web section 30, the bearing clearance 20 in the hydrostatic section 18 comprises the first bearing clearance C between the surface of the grinding wheel shaft 131 and the bearing surface section 22, and the second bearing clearance H between the surface of the grinding wheel shaft 131 and the web section 30.The size of the second bearing clearance H is set to be larger than the size of the first bearing clearance C. Therefore, the lubricating solution R, which flows through the second bearing clearance H when the grinding wheel shaft 131 is rotatably supported, forms a laminar flow along the direction of rotation of the grinding wheel shaft 131. The lubricating solution R in the side groove sections 42 in the pocket 24 flows in the opposite direction to the direction of rotation of the grinding wheel shaft 131, while adverse effects on the laminar flow through the second bearing clearance H are suppressed, and then returns to the channel 16. As in . Fig. As shown in Figure 8, the energy consumption was therefore lower regardless of whether water, an aqueous solution or low-viscosity mineral oil was used as the lubricating solution R.

[0028] In the hydrostatic bearing device of the exemplary embodiment, the hydrostatic section 18 has the web sections 30, each of which projects from the bottom section of the corresponding pocket 24 towards the surface of the grinding wheel shaft 181 as described above, and which have the end face 32, which faces the surface of the grinding wheel shaft 131, and the groove section 40, which lies between the web section 30 and the edge 28 of the pocket 24. The groove section 40 has the side groove sections 42, which are located on both sides of the web section 30 such that they extend in the circumferential direction, the upstream groove section 44, which is positioned upstream in the direction of rotation of the grinding wheel shaft 131, and the downstream groove section 46, which is positioned downstream in the direction of rotation.The groove section 40 also has the channel 16 (supply path) which communicates with the upstream groove section 44 to supply the hydrostatic section 18 with the lubricating solution R. Consequently, the lubricating solution R flows in the direction of rotation of the grinding wheel shaft 131 over the end face 32 and in the side groove sections 42 in the opposite direction to the rotation of the grinding wheel shaft 131. This makes it less likely that the flow over the end face 32 and the flow in the side groove sections 42 will interfere with each other. Thus, a possible increase in the velocity gradient of the fluid in the pockets 24 in the hydrostatic bearing device is suppressed, which allows for a reduction in energy loss.If the density of the lubricating solution R is denoted by p, the viscosity coefficient of the lubricating solution R is denoted by µ, the circumferential speed of the grinding wheel shaft 131 is denoted by U, and the size of the second bearing clearance is denoted by H, the Reynolds number for the second bearing clearance H is expressed by Re = ρUH / µ, and for the flow of the lubricating solution R through the second bearing clearance H when the grinding wheel shaft 131 is rotatably supported, Re < 2000. This means that, in connection with the flow of the lubricating solution R through the second bearing clearance H, a high fluid shear resistance is less likely to occur, which allows the energy loss to be suppressed.

[0029] The lubricating solution R is suitablely water or an aqueous solution in which 90% or more of its composition is water, or low-viscosity mineral oil.

[0030] The lubricating solution R, which flows through the second bearing clearance H when the grinding wheel shaft 131 is rotatable, forms a laminar flow along the direction of rotation of the grinding wheel shaft 131. A portion of this laminar flow of lubricating solution R moves via the upstream groove section 44 and the side groove sections 42 to the upstream groove section 44 containing the supply path. Consequently, the web section 30 separates the laminar flow through the second bearing clearance H from the flow in the side groove sections 42 in the direction opposite to the direction of rotation. This makes it less likely that the laminar flow and the flow in the direction opposite to the direction of rotation will interfere with each other. Therefore, a potential increase in the velocity gradient of the fluid in the pocket 24 is suppressed, which further reduces energy loss.

[0031] The hydrostatic bearing device designed as described above is suitablely used for a machine tool main spindle device which supports a machine tool main spindle in such a way that the machine tool main spindle is rotatable.

[0032] One embodiment of the invention has been described. However, the hydrostatic bearing device and the machine tool main spindle device with the hydrostatic bearing device are not limited to this embodiment and can be implemented in various forms.

Claims

[1] Hydrostatic bearing device with: a rotating wave (131); and a bearing metal (14) with a hydrostatic section (18) which allows the rotating shaft (131) to be rotatably supported, wherein the hydrostatic section (18) comprises a bearing clearance (20) located between a surface of the rotating shaft (131) and the bearing metal (14) and filled with a lubricating solution (R), a bearing surface section (22) facing the surface of the rotating shaft (131), a plurality of pockets (24) recessed side by side in a circumferential direction of the bearing surface section (22), and web sections (30) each projecting from a bottom section (26) of a corresponding pocket (24) towards the surface of the rotating shaft (131) and having an end face (32) facing the surface of the rotating shaft (131) and a groove section (40) located between the web section (30) and an edge (28) of the pocket (24). the groove section (40) side groove sections (42) which are located on both sides of each web section (30) such that they extend in the circumferential direction, have an upstream groove section (44) which is positioned upstream in a rotational direction of the rotating shaft (131), and a downstream groove section (46) which is positioned downstream in the rotational direction, the groove section (40) has a supply path (16) that communicates with the upstream groove section (44) to supply the hydrostatic section (18) with the lubricating solution (R), the bearing clearance (20) has a first bearing clearance (C) between the surface of the rotating shaft (131) and the bearing surface section (22) and a second bearing clearance (H) between the surface of the rotating shaft (131) and the end face (32), the size of the second storage game (H) is designed to be larger than the size of the first storage game (C), when the density of the lubricating solution (R) is denoted by ρ, a viscosity coefficient of the lubricating solution (R) is denoted by µ, a circumferential speed of the rotating shaft (131) is denoted by U and the size of the second bearing play (H) is denoted by H, a Reynolds number for the second bearing clearance (H) is expressed by Re = ρUH / µ and for a flow of the lubricating solution (R) that takes place through the second bearing clearance (H) when the rotating shaft (131) is rotatably supported, Re < 2000 applies. [2] Hydrostatic bearing device according to claim 1, wherein the lubricating solution (R) is water or an aqueous solution in which 90% or more of its composition is water, or low-viscosity mineral oil. [3] Hydrostatic bearing device according to claim 1 or 2, wherein the lubricating solution (R) flowing through the second bearing clearance (H) when the rotating shaft (131) is rotatably supported forms a laminar flow along the direction of rotation of the rotating shaft (131) and a part of the laminar flow of the lubricating solution (R) moves via the side groove sections (42) to the upstream groove section (44) with the supply path (16). [4] Machine tool main spindle device with the hydrostatic bearing device according to one of claims 1 to 3, which supports a machine tool main spindle in a machine tool (10) such that the machine tool main spindle is rotatable.

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