Gas bearing spindle and gas bearing assembly for a gas bearing spindle

Abstract

A gas bearing assembly (1) for a gas bearing mandrel. The assembly includes a housing portion (11) and an inner radial bearing portion (12) disposed within the housing portion (11) and elastically mounted relative to the housing portion (11). The inner radial bearing portion (12) includes an inner housing bearing portion (12a) having a bearing surface, and an intermediate sleeve portion (14) disposed between the inner housing bearing portion (12a) and the housing portion (11). A liquid coolant channel (7) is disposed between the inner housing bearing portion (12a) and the intermediate sleeve portion (14). The gas bearing assembly also includes protrusions (113a) and slots (113b) arranged to maintain the housing portion (11) and the inner bearing portion (12) against relative rotation.

Description

Technical Field

[0001] This invention relates to gas bearing mandrels and gas bearing assemblies for gas bearing mandrels. Background Technology

[0002] Of particular interest are gas bearing spindles suitable for use in high-speed drilling applications, such as PCB (printed circuit board) drilling. In PCB drilling machines, there is a desire for machines capable of drilling holes of a wide range of diameters (corresponding to a wide range of speeds). Therefore, for example, there is a desire to provide a machine capable, for instance, of drilling a 6.3mm diameter hole at approximately 15,000-20,000 rpm at one end of the scale, while still being able to drill holes of approximately 0.1mm to 0.2mm diameter at approximately 200,000 rpm or 350,000 rpm at the other end of the scale. Furthermore, these holes need to be drilled with high precision and typically require the provision of high-quality holes on the printed circuit board.

[0003] When drilling at most (if not all) speeds, radial and / or axial vibrations in the equipment tend to degrade the quality of the drilled hole. Providing damping to suppress this vibration can significantly help reduce this problem.

[0004] Furthermore, by suppressing the occurrence of half-velocity whirl within the bearing film, this damping allows the shaft to reach significantly higher maximum speeds. (Half-velocity whirl is a well-understood resonance state that occurs in supercritical gas hydrostatic bearing systems, and its occurrence typically leads to spindle failure due to the unstable nature of the gas film. This occurs at approximately twice the critical speed of the bearing film.)

[0005] One existing method for providing damping is to mount the spindle bearing on a resilient O-ring. In this case, the bearing is, in principle, allowed to move radially and axially within a set constraint range as the shaft moves along with it. Therefore, the vibrational energy generated during drilling can be absorbed by the continuous deformation of the O-ring material, thus providing good damping for the shaft. However, a drawback of applying this technology to PCB spindles is that a significant amount of heat is generated inside the bearing due to film shear at the high speeds required for drilling very small holes. One way to overcome this problem is to provide cooling, such as water cooling, to prevent overheating and control the thermal expansion of the film gap.

[0006] However, this is not without its challenges—cooling needs to be provided in the right place, and the damping effect needs to be maintained. Summary of the Invention

[0007] The applicant has developed a mandrel to provide at least some of these functions, wherein an inner bearing portion is supported in an O-ring relative to a housing portion, and the inner bearing portion actually has an internal coolant channel. This is due to the inner bearing portion having an intermediate section or sleeve, an inner housing bearing portion, and a coolant channel disposed between them.

[0008] Such bearing assemblies can provide effective support for shafts, such as those in PCB drilling mandrels, but there is a constant drive to find more efficient and smaller systems, and a desire to reduce the complexity of such mandrels and improve their reliability, especially at higher speeds.

[0009] One aspect to consider is the need to ensure a complete and secure coolant flow path through the spindle, and particularly the bearing assembly. In some existing designs, a problem arises where, under extreme loads or failure modes, the inner bearing portion may rotate relative to the housing portion. This, in turn, can disrupt the integrity of the coolant feed path and lead to catastrophic failure of the bearing spindle. Existing solutions to these problems have included providing anti-rotation features to resist this relative rotation—these features work effectively but impose practical limitations on the size of the bearing assembly and may increase the number of parts / complexity of the assembly.

[0010] Therefore, it is desirable to produce alternative gas bearing assemblies and / or mandrels that include gas bearing assemblies, which are designed to address at least some of these considerations.

[0011] According to a first aspect of the invention, a gas bearing assembly for a gas bearing mandrel is provided, the assembly comprising a housing portion and an inner radial bearing portion disposed within and elastically mounted relative to the housing portion, the inner radial bearing portion comprising an inner housing bearing portion having a bearing surface, and an intermediate sleeve portion disposed between the inner housing bearing portion and the housing portion, wherein a liquid coolant channel is disposed between the inner housing bearing portion and the intermediate sleeve portion, and the gas bearing assembly further comprising a lug and slot arrangement to retain the housing portion and the inner bearing portion against relative rotation.

[0012] This helps ensure resistance to relative rotation between the housing portion and the inner radial bearing portion, which could jeopardize the flow path of the liquid coolant into the liquid coolant passages, while enabling a particularly compact integral bearing assembly design. This, in turn, helps minimize the mass of the inner radial bearing portion, and thus improves the stability and efficiency of the bearing assembly, providing corresponding benefits to the spindle in which the bearing assembly is located.

[0013] The arrangement of bumps and slots can include: i) at least one protrusion, said at least one protrusion being disposed on one of the housing portion and the inner radial bearing portion; and ii) At least one corresponding slot, which is provided on the other of the housing portion and the inner radial bearing portion and is arranged to receive the corresponding protrusion.

[0014] The portion of the housing and the inner radial bearing portion that has the protrusion may include a main body portion. The protrusion may be integral with the main body portion. The protrusion may be a machined part. As an example, the protrusion may be provided by CNC machining. Machining can form a workpiece that becomes a blank of the main body portion. The workpiece includes the material that will become the main body and the material that will become the protrusion.

[0015] The main body and the bumps can be made from a single piece of material.

[0016] In one set of embodiments, a protrusion is provided on the inner radial bearing portion. In this case, the protrusion may be provided on one of the inner housing bearing portion and the intermediate sleeve portion. The protrusion may be integrally formed with one of the inner housing bearing portion and the intermediate sleeve portion.

[0017] In some embodiments, the inner housing bearing portion may include a housing body portion and a protrusion. In this case, the housing body portion and the protrusion may be made of a single piece of material. The inner housing bearing portion may be made of a single piece of material.

[0018] In some embodiments, the intermediate sleeve portion may include a sleeve body portion and a protrusion. In this case, the sleeve body portion and the protrusion may be made of a single piece of material. The intermediate sleeve portion may be made of a single piece of material.

[0019] The bump can extend axially relative to the axis of the bearing assembly. The bump can extend axially away from the body portion where the bump is located. The bump can have a cross-section with an annular fan shape. Preferably, the bump extends axially relative to the axis of the bearing assembly and has a cross-section with an annular fan shape. This shape corresponds to a portion of the curved sidewall of a (relatively thin-walled) hollow cylinder.

[0020] The housing portion may include a plate defining a notch for receiving a protrusion. The notch may be arc-shaped. The notch may have an annular or fan-shaped shape. In some cases, the notch may be a aperture within the plate, with its sidewalls entirely within the plate. In other cases, the notch may be a cutout at the periphery of the plate. This helps reduce the material used in the bearing assembly, thereby reducing its weight and simplifying manufacturing.

[0021] The housing portion may include a main body portion having an aperture for receiving an inner radial bearing portion. A plate may be mounted on the main body portion of the housing portion.

[0022] The slot and the bump can be arranged such that when the bump is received in the slot, a gap is created between the sidewall of the slot and the bump, so that the bump does not need to contact the sidewall of the slot. This means that during normal operation of the bearing assembly, there is no need for contact between the bump and the sidewall of the slot. Such contact could impair the performance of the bearing assembly. On the other hand, if the housing and the inner radial bearing portion are subjected to forces that tend to cause relative rotation between the housing and the inner radial bearing portion, contact may occur between the bump and the sidewall of the slot, thereby resisting a harmful degree of relative rotation.

[0023] When the slot has an annular fan shape, the slot can be defined by sidewalls comprising at least one side (e.g., at least one curved wall portion) and a pair of endwall portions. In this case, relative rotation will tend to be resisted by the contact between the protrusion and at least one of the pair of endwall portions. The at least one curved wall portion may extend along a circumferential path around the axis of the bearing assembly. The endwall portions may be transverse to the at least one side. The endwall portions may be radial endwalls or at least generally radially extending.

[0024] The inner radial bearing portion can be elastically mounted relative to the housing portion via at least one damping O-ring. In other words, the bearing assembly may include at least one damping O-ring to facilitate elastic mounting.

[0025] The at least one damping O-ring can be arranged to surround the inner radial bearing portion. The at least one damping O-ring can be arranged such that its axis is substantially parallel to, and preferably substantially coincides with, the axis of the inner radial bearing portion. The at least one damping O-ring can be disposed on the intermediate sleeve portion.

[0026] Preferably, a pair of damping O-rings are provided between the housing portion and the inner radial bearing portion, and surround the inner radial bearing portion. The pair of damping O-rings may be axially spaced apart from each other. The pair of damping O-rings may be arranged toward corresponding opposite ends of the inner radial bearing portion. The pair of damping O-rings may be provided on the intermediate sleeve portion.

[0027] In preferred embodiments, the intermediate sleeve portion defines a sleeve inlet for allowing the liquid coolant to flow into the channel and a sleeve outlet for allowing the liquid coolant to flow out of the channel.

[0028] The housing portion may include an inlet port for supplying coolant to the coolant passage via the sleeve inlet, and a discharge port for receiving coolant exiting the coolant passage via the sleeve outlet.

[0029] The sleeve inlet can be located in the outer curved surface of the intermediate sleeve section.

[0030] The sleeve outlet can be located in the outer curved surface of the intermediate sleeve section.

[0031] The gas bearing assembly may include at least one auxiliary O-ring arranged around an inlet to or an outlet of a liquid coolant passage located between the inner housing bearing portion and the intermediate sleeve portion. There may be a pair of auxiliary O-rings—one arranged around the inlet of the liquid coolant passage and one around the outlet. The auxiliary O-ring, or each auxiliary O-ring, may be located on the intermediate sleeve portion. The auxiliary O-ring, or each auxiliary O-ring, may be arranged with its main axis transverse to the axis of the gas bearing assembly. The main axis of the auxiliary O-ring, or each auxiliary O-ring, may be oriented radially along the gas bearing assembly.

[0032] The intermediate sleeve portion may include an O-ring receiving groove in the outer curved surface of the intermediate sleeve portion, the groove being configured to surround the sleeve inlet.

[0033] The intermediate sleeve portion may include an O-ring receiving groove in the outer curved surface of the intermediate sleeve portion, the groove being configured to surround the sleeve outlet.

[0034] The auxiliary O-ring receiving groove, or each O-ring receiving groove, can be circular, and its center coincides with the center of the inlet / outlet it surrounds.

[0035] The auxiliary O-ring receiving groove, or each O-ring receiving groove, can be CNC machined into the outer curved surface of the intermediate sleeve section.

[0036] The liquid coolant passage may be partially defined by the surface of the intermediate sleeve portion. The liquid coolant passage may also be partially defined by the surface of the inner housing bearing portion.

[0037] The inner bearing housing can be generally annular. The sleeve can be generally annular.

[0038] The inner housing bearing portion can be tightly fitted inside the sleeve—this can be an interference fit.

[0039] The housing portion may have an orifice in which the inner radial bearing portion is disposed. The inner radial bearing portion may have an outwardly curved surface facing the orifice, and a gap may be provided between the outwardly curved surface of the inner radial bearing portion and the orifice. The outwardly curved surface of the inner radial bearing portion may be the outwardly curved surface of a sleeve. The gap may be maintained by at least one elastic damping member (such as the at least one damping O-ring).

[0040] The orifice can be cylindrical. The outer curved surface of the inner radial bearing portion can be cylindrical.

[0041] The bearing face will typically include at least one series of gas outlets for supplying gas to form a gas film between the bearing face and the shaft disposed in the bearing assembly.

[0042] Each gas outlet may include a jet port.

[0043] The bearing assembly may include two series of gas outlets spaced apart from each other in the axial direction, with a liquid coolant passage located axially between the two series of gas outlets.

[0044] The liquid coolant channel can be an annular channel, which may have an axis that coincides with the main axis of the bearing assembly.

[0045] Preferably, the protrusion is disposed on the intermediate sleeve portion.

[0046] It is advantageous to place the bump on the intermediate sleeve portion because it maximizes the radius of the bump's operation. This, in turn, reduces the resistance the bump needs to exert against the specific relative torsional forces that occur between the housing and the inner radial bearing portion.

[0047] Furthermore, it minimizes the distance the housing needs to extend toward the axis of the bearing assembly to allow for the interaction between the slots and bumps. Therefore, for example, in the case where the slots are located within the plate of the housing, it minimizes the distance the plate needs to extend toward the axis of the bearing assembly. This can help to further reduce the mass of the bearing assembly.

[0048] When the intermediate sleeve portion includes at least one CNC-machined O-ring receiving groove, it is advantageous to set the protrusion on the intermediate sleeve portion, as this facilitates the CNC machining of the protrusion.

[0049] The bump can be sized and arranged such that the amount of extension of the bump in one direction is greater than the amount of extension of the bump in at least one direction perpendicular to that direction, in which the bump is arranged to resist forces to keep the housing portion and the inner bearing portion against relative rotation.

[0050] The bump can be sized and arranged such that the length of the bump in the circumferential direction around the axis of the bearing assembly is greater than the thickness of the bump in the radial direction of the bearing assembly.

[0051] The above feature can be an example of the feature preceding the above feature.

[0052] These two features help to maximize the strength of the bump in the direction in which strength is required to resist relative rotation, while minimizing its overall size and mass.

[0053] The arrangement of bumps and slots can include multiple bumps and corresponding multiple slots.

[0054] The bumps among multiple bumps can be angularly spaced (e.g., equally spaced) around the main axis of the radial bearing assembly. Similarly, the slots among multiple slots can be angularly spaced (e.g., equally spaced) around the main axis of the radial bearing assembly. Multiple bumps can be provided to align with multiple slots.

[0055] In a particular set of implementations, a pair of bumps and a corresponding pair of slots may be provided. The bumps in the pair of bumps may be radially opposite. The slots in the pair of slots may be radially opposite.

[0056] By appropriately selecting the size and arrangement of the bumps, the number of required bumps and slots can be minimized.

[0057] According to another aspect of the invention, a gas bearing mandrel is provided, the gas bearing mandrel comprising a mandrel body portion, at least one gas bearing assembly as defined above housed in the mandrel body portion, and a journal support for rotation within the at least one gas bearing assembly.

[0058] In some embodiments, the spindle includes a spindle coolant flow path from the spindle coolant inlet to the spindle coolant outlet, and the gas bearing assembly includes a component coolant flow path from the component coolant inlet to the component coolant outlet, and the component coolant flow path forms part of the spindle coolant flow path.

[0059] Typically, a spindle includes a motor for rotating a shaft relative to a gas bearing assembly.

[0060] In one set of embodiments, the spindle may include two radial air bearings and one axial air bearing. These embodiments may further include a motor for rotatably driving the shaft relative to the gas bearing assembly, and each of the gas bearing assembly and the motor may be supplied with coolant through a spindle coolant flow path.

[0061] Gas bearing spindles can be drilling spindles, such as PCB drilling spindles.

[0062] Gas bearing assemblies can be air static pressure bearing assemblies.

[0063] Typically, the gas used in gas bearing assemblies is air.

[0064] Typically, the coolant used in a spindle is water.

[0065] According to another aspect of the invention, a drilling machine, such as a PCB drilling machine, is provided, the drilling machine including a drilling mandrel as defined above and a cooling system for feeding coolant through a mandrel coolant flow path.

[0066] Note that, in summary, and with any necessary modifications to the wording, all further features defined after any aspect of the invention above can be applied as further features of all other aspects of the invention defined above. For the sake of brevity, these further features are not repeated after each aspect of the invention. Attached Figure Description

[0067] Embodiments of the invention will now be described by way of example only with reference to the accompanying drawings, wherein: Figure 1 A schematic diagram illustrates a PCB drilling machine including a drilling gas bearing mandrel; Figure 2 schematically shown Figure 1 Drilling gas bearing mandrel; Figure 3 This schematically illustrates a method that can be used for Figure 2 Existing bearing assemblies for drilling mandrels of the type shown; Figure 4 schematically shown Figure 2 The bearing assembly of the drilling mandrel; Figure 5A It shows Figure 4 An end view of a portion of the bearing assembly shown. Figure 5B It shows Figure 5A The section shown is a cross-section along line VB-VB; Figure 6 schematically shown Figure 4 , Figure 5A and Figure 5B The inner radial bearing portion of the bearing assembly shown; and Figure 7 An alternative inner radial bearing portion is schematically shown, which can be used with... Figure 4 , Figure 5A and Figure 5B In bearing assemblies similar to those shown. Detailed Implementation

[0068] Figure 1 A PCB drilling machine is shown in a highly schematic form, comprising a high-speed PCB drilling mandrel S mounted on a main machine unit U, and a cooling system C including a coolant pump P for delivering coolant to the mandrel S via inlet and return feed lines L.

[0069] Figure 2The high-speed PCB drilling mandrel S is shown in more detail. This PCB drilling mandrel is designed for use both at high speeds (e.g., speeds up to about 200,000 rpm, 350,000 rpm or even higher) and at relatively low speeds (such as 15,000 to 20,000 rpm).

[0070] The PCB drilling mandrel is an air bearing mandrel and includes two radial air bearing assemblies 1 housed within the main body portion 2 of the mandrel. The shaft 3 carrying the tool holder 4 is journal-supported within the radial air bearings 1. A motor 5, consisting of a stator 51 arranged in the main body portion 2 and windings 52 embedded in the shaft 4, is provided for rotatably driving the shaft 3 relative to the main body portion 2. The tool holder 4 is arranged to hold a tool, in this example, a drilling tool for drilling holes in PCB material. An axial air bearing assembly 6 is provided, which acts on a thrust guide plate 31 located at the distal end of the shaft 3.

[0071] The rear end of the spindle is provided with a tool release actuation mechanism 32, which acts on the tool holder 4 through an actuation rod 33 extending inside the spindle 3.

[0072] The drilling mandrel in Figure 2 is conventional to the extent described above. Therefore, for the sake of brevity, a detailed description of its overall structure and operation is omitted in this specification. It should be understood that the following is a well-known technique: providing an air-bearing mandrel that includes a suitable air bearing and a motor drive, as well as a tool holder for holding the tool to be driven.

[0073] This application relates primarily to various aspects of radial air bearing assembly 1.

[0074] exist Figure 2 In each radial air bearing assembly 1 of the mandrel shown, there are two main components. The first is an outer bearing housing portion 11, within which an inner radial bearing portion 12 is mounted. Both the outer bearing housing portion 11 and the inner radial bearing portion 12 are generally annular components. Therefore, the inner radial bearing portion 12 is mounted within the orifice B of the outer bearing housing portion 11. However, a significant gap is provided between the outer curved surface of the inner radial bearing portion 12 and the inner curved surface of the orifice B of the outer bearing portion 11.

[0075] The inner radial bearing portion 12 is mounted within the outer bearing housing portion 11 via a pair of O-rings 13. One O-ring 13 is positioned towards one end of the bearing assembly 1, and the other O-ring 13 is positioned towards the other end of the bearing assembly 1. These O-rings 13 are used to elastically support the inner radial bearing portion 12 within the outer bearing housing portion 11.

[0076] Due to the gap between the two parts 11 and 12 mentioned above and the elastic properties of the O-ring 13, the inner radial bearing part 12 has a certain degree of freedom of movement in both the axial and radial directions relative to the outer bearing housing part 11.

[0077] Of course, when such movement occurs, the O-ring 13 will deform. This arrangement also applies to... Figure 2 Two bearing assemblies 1 are installed inside the spindle.

[0078] Therefore, when shaft 3 tends to vibrate during spindle operation, the inner radial bearing portion 12 can move on the O-ring 13, which absorbs this vibrational energy, thereby suppressing vibration in shaft 3. This, in turn, can lead to better drilling performance. As described in the introduction of this specification, there are existing systems that utilize this type of damping.

[0079] Generally speaking, as mentioned in the introduction, cooling is required for such bearings, and this needs to be done while maintaining the required flexible mounting level.

[0080] Also referencing Figure 4 In this radial bearing assembly 1, the inner radial bearing portion 12 includes an intermediate sleeve 14 and an inner housing bearing portion 12a, such that the intermediate sleeve 14 is disposed between the inner housing bearing portion 12a and the outer bearing housing portion 11.

[0081] In this spindle, the inner housing bearing portion 12a is generally annular, and the intermediate sleeve portion 14 is also generally annular. In this case, the intermediate sleeve portion 14 can be retracted and fitted onto the inner housing bearing portion 12a.

[0082] A coolant channel 7 in the form of an annular groove is provided in the inner radial bearing portion 12. Specifically, the coolant channel 7 is located between the inner housing bearing portion 12a and the intermediate sleeve portion 14. The coolant channel 7 is defined by the surface of the inner housing bearing portion 12a and the surface of the intermediate sleeve portion 14. Therefore, the coolant channel 7 is effectively isolated from the outer bearing housing portion 11 by the intermediate sleeve 14 located between the coolant channel 7 and the outer bearing housing portion 11. This means that during use, there is no direct contact, or rather, no mechanical contact, between the coolant supplied in the coolant channel and the surface of the orifice B of the outer bearing housing portion 11.

[0083] This helps ensure that there is no excessive mechanical coupling between the inner radial bearing portion 12 and the outer bearing housing portion 11, which could otherwise inhibit the elasticity of the installation.

[0084] Of course, however, coolant (usually water) must be fed into and out of the annular coolant passage 7 provided in the inner bearing section 12.

[0085] An inlet 71 is provided to enter the coolant passage 7, and an outlet 72 is provided to exit the coolant passage 7. Furthermore, the inlet 71 and outlet 72 are aligned with the supply port or inlet port 11a and discharge port 11b provided in the outer bearing housing portion 11.

[0086] Therefore, water can be fed into the coolant channel through the inlet port 11a, flow around the channel 7, and then flow out of the channel 7 through the outlet 72 and into the discharge port 11b.

[0087] It should be noted that the coolant passage 7 extends circumferentially around the inner bearing portion 12. In this arrangement, coolant flows into inlet 71 and then splits into two streams, flowing around both sides of the bearing assembly, before rejoining at outlet 72 to flow out of the inner bearing portion 12.

[0088] Surrounding the inlet 71 and outlet 72 are corresponding O-ring grooves 71a and 72a, each O-ring groove accommodating a corresponding O-ring 71b or 72b (see...). Figure 4 These O-rings 71b and 72b act as seals around the inlet 71 and outlet 72, respectively, abutting against the wall of the orifice B of the outer bearing housing portion 11 that they face, such as... Figure 4 visible.

[0089] As mentioned above, the O-rings 13 located at each end of the inner bearing portion 12 provide a resilient mount of the inner bearing portion 12 relative to the outer bearing housing portion 11 to provide the required damping. The O-rings 71b and 72b surrounding the inlet 71 and outlet 72 provide a seal between the inlet port 11a and the inlet 71, and between the outlet 72 and the discharge port 11b, without compromising this resilient mount. This is achieved by ensuring a suitable clearance between the surface of the intermediate sleeve 14 and the orifice B of the outer bearing housing portion 11 in this region, and by selecting appropriate O-rings 71b and 72b.

[0090] It should be noted that although the intermediate sleeve 14 is annular and has a generally cylindrical outer surface, the thickness of the annulus is not constant along the axial length of the sleeve 14. In particular, the outer diameter of the sleeve 14 is larger in the central zone forming the inlet 71 and outlet 72. Therefore, the outer curved surface of the sleeve 14 is stepped. For example... Figure 4 As seen in the diagram, this results in a smaller gap between the sleeve 14 and the orifice B of the outer bearing housing portion 11 in the central region of the bearing assembly 1 (i.e., the region where the inlet 71 and outlet 72 are located).

[0091] It should be noted that O-rings 71b and 72b surrounding the inlet 71 and outlet 72 are arranged on the outer surface of the intermediate sleeve portion 14, oriented such that the axis of the O-rings is substantially along the radial direction of the bearing assembly. At the same time, the main damping O-rings 13 are provided to surround the inner bearing portion 12 and are oriented such that their main axis is substantially coincident with the axis of the bearing assembly 1.

[0092] Of course, it should be remembered that radial bearing assembly 1 is an air bearing assembly. Therefore, in addition to sealing the corresponding water passages through the bearing assembly for cooling, it is also necessary to seal the air supply path for supplying air to the air bearing.

[0093] In this regard, it should be noted that the damping O-ring 13 (see [reference]) is located at either end of the bearing assembly 1. Figure 2 The sealing O-rings 71b and 72b surrounding the inlet 71 and outlet 72 also provide a sealing function to provide a suitable air supply passage for the air bearing.

[0094] For example Figure 4 As can be seen, the bearing assembly includes two series of jet ports 8, which are disposed on the bearing surface 12c of the inner housing bearing portion 12a. During operation, the jet ports 8 supply air to the air bearing to form the necessary air film between the bearing surface 12c and the shaft 3. It can be noted that the two series of jet ports 8 are axially spaced apart from each other, and the coolant passage 7, along with its inlet 71 and outlet 72, is axially positioned between these two series of jet ports.

[0095] Although the ability of the inner radial bearing portion 12 to rotate relative to the outer bearing housing portion 11 was initially considered a potential advantage of the drilling mandrel with the resiliently mounted inner radial bearing portion 12, in practice, the occurrence of such relative rotation has proven problematic in certain situations.

[0096] In particular, if such relative rotation occurs, the integrity of the coolant feed path used to supply coolant to the inner bearing section may be compromised, potentially causing coolant to leak into the bearing. Furthermore, if relative rotation has already cut off the air supply to the air bearing, leaving the air feed path unpressurized, water may enter the air feed path and other bearing components, potentially leading to catastrophic failure of the bearing and / or spindle.

[0097] Because of this, this type of spindle has been designed to include anti-rotation features.

[0098] Figure 3 An existing radial bearing assembly 1' of this type of mandrel manufactured by the applicant is shown.

[0099] The existing radial bearing assembly 1' has the same overall structure as the assembly 1 described above, and therefore includes an inner bearing portion 12, which comprises an inner housing bearing portion 12a and an intermediate portion 14, both of which are elastically mounted together in an outer bearing housing portion 11. The existing radial bearing assembly includes a plurality of axial anti-rotation pins 901 for resisting relative rotation between the inner bearing portion 12 and the outer bearing housing portion 11.

[0100] End cap 904 (by screw 905) is mounted to the remainder of outer bearing housing portion 11. It extends radially into the interior of the main bore B of outer bearing housing portion 11 so as to protrude at least partially beyond the end of inner bearing portion 12 (specifically, intermediate portion 14 and inner housing bearing portion 12a).

[0101] The inner peripheral edge 904a of the end cap 904 defines a plurality of (six in this case) slots 904b. Each of these slots receives a corresponding anti-rotation pin 901. One end of each pin 901 is received in its corresponding slot 904b, and the other end is received in a corresponding orifice 906 in the inner bearing portion 12 (specifically in the inner housing bearing portion 12a in this embodiment).

[0102] As determined by the applicant, minimizing the size and mass of the inner bearing portion 12 in this type of mandrel is particularly effective in improving the mandrel's performance in terms of operating efficiency and stability. This is especially true in the case of a radial air bearing at the very rear end of a mandrel comprising two radial air bearings and a thrust bearing located at the front or nose of the mandrel.

[0103] The above Figure 3 The arrangement can effectively prevent unwanted rotation between the inner bearing portion 12 and the outer bearing housing portion 11, but problems arise when attempting to reduce the size and / or mass of the bearing assembly, especially the inner bearing portion 12.

[0104] To achieve a certain size, an anti-rotation pin 901 is provided, which is fitted into an opening drilled into the inner bearing portion 12a, to provide a functional product that is easy to manufacture. However, as the size decreases, the pin becomes smaller and more difficult to handle in practice, and it also becomes difficult to find a position in the inner bearing portion 12 to accommodate the pin.

[0105] Therefore, the applicant sought to find an alternative to provide Figure 3 The anti-rotation feature is of the type shown. After exploring various approaches, the applicant has developed an alternative system, which will be specifically referenced below. Figure 4 , Figure 5A , Figure 5B and Figure 6 As described.

[0106] As mentioned above, Figure 4 One of the radial bearing assemblies 1 of the present invention is shown. Specifically, Figure 4 It shows Figure 2 The front radial bearing assembly 1 of the mandrel shown. The housing portion 11 of the front radial bearing assembly 1 includes a housing body portion 111, a plate 112, and a thrust plate 113 as part of the axial bearing device 6. The plate 112 is mounted to the housing body portion 111 by screws 114.

[0107] Figure 5A and Figure 5B Plate 112 together with inner radial bearing portion 12 is shown, but housing body portion 111 or thrust plate 113 in place is not shown. Figure 6 The inner radial bearing portion 12 is shown separately.

[0108] It will be noted that plate 112 corresponds to Figure 3 The end cap 904 is shown in the arrangement, but there are differences. For example... Figure 4 As seen, plate 112 is accommodated in a recess 111a provided at the end of the housing body portion 111. This helps to minimize the size and weight of the bearing assembly. Furthermore, compared to the cover portion 904 described above, the central aperture 112a provided in plate 112 is relatively large, such that the extension of plate 112 in the radial range of the inner radial bearing portion 12 is smaller than that of end cover 904. Furthermore, for example, by considering... Figure 5B As can be seen, one end 12a' of the inner housing bearing 12a extends into the aperture 112a of the plate 112. This can further contribute to the compactness of the design. The end 12a' may be tapered, such that the distal end of the tapered portion has a smaller outer diameter than the body of the inner housing bearing 12a.

[0109] In such Figure 4 , Figure 5A and Figure 5B In the preferred embodiment shown, the front radial bearing assembly 1 includes a bump and slot arrangement 113 for resisting relative rotation between the bearing housing portion 11 and the inner radial bearing portion 12.

[0110] In this embodiment, a pair of protrusions 113a are provided on the intermediate sleeve 14, and a pair of corresponding slots 113b are provided on the plate 112. The protrusions 113a and slots 113b are aligned with each other such that the first protrusion 113a is received in the first slot 113b, and the second protrusion 113a is received in the second slot 113b. The interaction between the protrusions 113a and the slots 113b serves to resist unwanted relative rotation between the bearing housing portion 11 and the inner radial bearing portion 12.

[0111] Each protrusion 113a is integrally formed with the remainder of the intermediate sleeve 14. In this embodiment, the intermediate sleeve 14 has a body portion 14a, and both the body portion 14a and the pair of protrusions 113a are made of a single piece of material. Figure 6 In the image, an O-ring groove 71a and a pair of protrusions 113a can be seen surrounding the coolant inlet 71 located on the outer curved surface of the intermediate sleeve 14. O-ring grooves 71a and 72a are provided. Figure 6 A convenient way to do this (not visible in the middle) is to CNC machine the material of the intermediate sleeve 14. Therefore, one advantage of setting the protrusion 113a on the intermediate sleeve 14 is that the protrusion 113a and the O-ring grooves 71a, 72a can be CNC machined as part of a common manufacturing step to form a workpiece as a blank of the intermediate sleeve 14.

[0112] Furthermore, since the protrusion 113a is integrally formed with the sleeve 14, a robust design can be achieved with minimal material and a minimal number of separate parts. Additionally, the need for separate pins, as seen in existing designs, is avoided.

[0113] Perhaps more importantly, there is no need to search for a location on the inner radial bearing section 12 that can provide an opening to accommodate these pins.

[0114] In general, this means providing a compact and efficiently manufacturable arrangement.

[0115] The use of protrusion 113a facilitates the provision of suitable anti-rotation features on the intermediate sleeve 14. This is advantageous because it means that the anti-rotation features are set more readily than if they were set on the inner housing bearing portion 12a (as in...). Figure 3 In the case of components (such as bearing housing portion 11 and inner radial bearing portion 12), the protrusion 113a occupies a radially outward position. This allows the protrusion 113a to better resist a certain degree of torsional force between the bearing housing portion 11 and the inner radial bearing portion 12.

[0116] The use of bump 113a further facilitates the selection of the size of bump 113a to provide resistance to forces in the desired direction while minimizing its size / mass.

[0117] Each protrusion 113a is generally plate-shaped. Each protrusion 113a extends axially away from the main body portion 14a of the intermediate sleeve 14. Each protrusion 113a has a cross-section in the shape of an annular fan. Therefore, the overall shape of each protrusion 113a corresponds to a portion of the curved sidewall of a (relatively thin-walled) hollow cylinder.

[0118] Each protrusion 113a is sized and arranged such that the extension of the protrusion 113a in a direction perpendicular to the force resistance is greater than the thickness of the protrusion 113a in the direction perpendicular to the force resistance. In this direction, the protrusion is arranged to resist the force so that the housing portion 11 and the inner bearing portion 12 resist relative rotation. Specifically, each protrusion 113a has a length "L" in the circumferential direction about the axis of the bearing assembly, which is greater than the thickness "T" of the protrusion in the radial direction of the bearing assembly 1 (see...). Figure 6 ).

[0119] This means that strength can be provided in the desired direction while mass is minimized.

[0120] Each slot 113b has an annular fan shape. In some cases, the slot can be provided as a hole in plate 113, with its sidewalls entirely within the plate. In this embodiment, each slot 113b is provided as a cutout at the periphery of the hole 112a in plate 112b. This helps reduce the material used in the bearing assembly and thus its weight, and simplifies manufacturing.

[0121] Each slot 113b is defined by sidewalls, which include a curved wall portion 113c and a pair of end wall portions 113d. The curved wall portion 113c extends circumferentially about the axis of the bearing assembly. The end wall portions 113d are transverse thereto.

[0122] The slots 113b and protrusions 113a are arranged such that when each protrusion 113a is received in its respective slot 113b, a clearance is provided between the sidewalls 113c, 113d of the slot 113b and the protrusion 113a, so that the protrusion 113a does not need to contact the sidewall of the slot 113b. This means that during normal operation of the bearing assembly 1, there is no need for contact between the protrusion 113a and the sidewall of the slot 113b. Such contact could impair the performance of the bearing assembly 1. On the other hand, if the housing portion 11 and the inner radial bearing portion 12 are subjected to forces that may tend to cause relative rotation between them, contact may occur between the protrusion 113a and the sidewall of the slot 113b, thereby resisting a harmful degree of relative rotation.

[0123] When the protrusion 113a is received in the slot 113b and subjected to relative torsional force, undesirable relative rotation tends to be resisted by the contact between the protrusion 113a and at least one of the pair of end wall portions 113d.

[0124] Although not shown separately, but Figure 2 The rear radial bearing assembly 1 of the spindle shown similarly includes a housing body portion 111 and a plate 112, and is provided with a lug and slot arrangement 113 as previously described with respect to the front radial bearing assembly.

[0125] Although a pair of bumps 113a and corresponding slots 113b are provided in this embodiment, in alternative embodiments, different numbers of bumps 113a and / or slots 113b may be provided.

[0126] Figure 7 An alternative form of the inner radial bearing portion 12' is shown separately, which is similar to Figure 6 As shown, it can be used in gas bearing assemblies similar to those described above. The inner radial bearing portion 12' is similar to the one described above regarding... Figures 4 to 6 Compared to the described inner radial bearing section, the only difference is that the O-ring groove 71a around the coolant inlet 71, the O-ring groove 72a around the coolant outlet 72, and the corresponding O-rings 71b and 72b are absent in the above arrangement. Instead, they are replaced by a pair of circumferential O-ring grooves 73 and corresponding O-rings (not shown).

[0127] Circumferential O-ring grooves 73 are provided in the outer curved surface of the intermediate sleeve 14. These grooves 73 are axially spaced (relative to the axis of the intermediate sleeve 14), with the coolant inlet 71 and coolant outlet 72 located within the axial spacing between these grooves 73. The grooves 73 are circular, with their centers aligned with the axis of the intermediate sleeve 14. Corresponding O-rings (not shown) are similarly aligned with the axis of the intermediate sleeve 14 when mounted onto the sleeve 14. The sealing purpose remains the same—to seal and isolate the inlet and outlet of the coolant passage 7 from the rest of the assembly. This sealing scheme provides a poor direct seal, allowing coolant to potentially remain in the band surrounding the intermediate sleeve 14 between the O-ring grooves 73. This, in turn, may be expected to reduce bearing (e.g., damping) performance. However, if this can be tolerated, there are manufacturing advantages, as machining the circumferential grooves 73 may be more advantageous than machining... Figure 6 The grooves 71a and 72a in the inner radial bearing portion 12 shown have a simpler manufacturing process and, for example, can avoid the use of CNC machining.

Claims

1. A gas bearing assembly for a gas bearing mandrel, the assembly comprising a housing portion and an inner radial bearing portion, the inner radial bearing portion being disposed within the housing portion and elastically mounted relative to the housing portion, the inner radial bearing portion comprising an inner shell bearing portion having a bearing surface, and an intermediate sleeve portion disposed between the inner shell bearing portion and the housing portion, wherein a liquid coolant channel is disposed between the inner shell bearing portion and the intermediate sleeve portion, and The gas bearing assembly further includes a bump and slot arrangement to keep the housing portion and the inner bearing portion resisting relative rotation.

2. The gas bearing assembly according to claim 1, wherein the arrangement of the protrusions and slots comprises: i) At least one protrusion, said at least one protrusion being disposed on one of the housing portion and the inner radial bearing portion; as well as ii) At least one corresponding slot, which is provided on the other of the housing portion and the inner radial bearing portion and is arranged to receive the corresponding protrusion.

3. The gas bearing assembly according to claim 2, wherein one of the housing portion and the inner radial bearing portion having the protrusion includes a main body portion, and the protrusion is integral with the main body portion.

4. The gas bearing assembly of claim 3, wherein the body portion and the protrusion are made of a single piece of material.

5. The gas bearing assembly according to any one of claims 2 to 4, wherein the protrusion is disposed on the inner radial bearing portion.

6. The gas bearing assembly according to claim 5, wherein the protrusion is disposed on the intermediate sleeve portion.

7. The gas bearing assembly according to any one of claims 2 to 6, wherein the bump extends axially away from the body portion on which the bump is provided.

8. The gas bearing assembly according to any one of claims 2 to 7, wherein the bump has a cross-section in the shape of an annular fan.

9. The gas bearing assembly according to any one of claims 2 to 8, wherein the protrusion is sized and arranged such that the protrusion extends in one direction more than the protrusion extends in at least one direction perpendicular to that direction, in which the protrusion is arranged to resist forces to keep the housing portion and the inner bearing portion against relative rotation.

10. The gas bearing assembly according to any one of claims 2 to 9, wherein the bump is sized and arranged such that the length of the bump in the circumferential direction about the axis of the bearing assembly is greater than the thickness of the bump in the radial direction of the bearing assembly.

11. The gas bearing assembly according to any one of claims 2 to 10, wherein the housing portion includes a plate defining a slot for receiving the protrusion.

12. The gas bearing assembly according to any one of the preceding claims, wherein the bump and slot arrangement comprises a plurality of bumps and a corresponding plurality of slots.

13. The gas bearing assembly of claim 12, wherein the protrusions of the plurality of protrusions are angularly spaced around the main axis of the radial bearing assembly, for example, at equal intervals.

14. The gas bearing assembly of claim 13, wherein a pair of protrusions and a corresponding pair of slots are provided, the protrusions of the pair of protrusions being radially opposite each other, and the slots of the pair of slots being radially opposite each other.

15. The gas bearing assembly according to any one of the preceding claims, wherein the inner radial bearing portion is elastically mounted relative to the housing portion by at least one damping O-ring.

16. The gas bearing assembly according to any one of the preceding claims, wherein the intermediate sleeve portion defines a sleeve inlet for allowing inflow into a liquid coolant passage and a sleeve outlet for allowing outflow from the liquid coolant passage, the sleeve inlet and sleeve outlet being disposed on an outer curved surface of the intermediate sleeve portion, and The gas bearing assembly includes a pair of auxiliary O-rings, one auxiliary O-ring arranged around the inlet of the liquid coolant channel and the other auxiliary O-ring arranged around the outlet of the liquid coolant channel. Each auxiliary O-ring is disposed on the intermediate sleeve portion and its main axis is perpendicular to the axis of the gas bearing assembly. The intermediate sleeve portion includes a pair of corresponding O-ring receiving grooves on its outer curved surface, one O-ring receiving groove being arranged around the sleeve inlet and the other O-ring receiving groove being arranged around the sleeve outlet, each O-ring receiving groove being CNC machined in the outer curved surface of the intermediate sleeve portion.

17. A PCB drilling gas bearing mandrel, comprising a mandrel body portion, at least one gas bearing assembly according to any one of the preceding claims housed within the mandrel body portion, and a journal support for rotation within the at least one gas bearing assembly.

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