Dense bead shaft system for laser tracking measurement system

Abstract

The utility model discloses a dense bead shaft system for a laser tracking measurement system, and relates to the technical field of dense bead shaft systems. The radial retainer is provided with a plurality of radial steel balls and is arranged outside the main shaft in a sleeving manner; the first thrust frame is provided with a plurality of end surface steel balls and is arranged outside the main shaft in a sleeving manner; the second thrust frame is provided with a plurality of supporting steel balls and is arranged outside the main shaft in a sleeving manner; and the first thrust frame and the second thrust frame are respectively positioned outside the corresponding end parts of the radial retainer. A plurality of radial steel balls are mounted on the radial retainer to form a radial dense ball bearing, and the first thrust frame and the second thrust frame are arranged outside the two ends of the radial retainer respectively, so that the first thrust bearing, the radial dense ball bearing and the second thrust bearing form an I-shaped structure, the radial and axial motion errors of the dense ball shaft system are reduced, and the service life of the dense ball shaft system is prolonged. Therefore, the rotation precision is high, and the rotation precision requirement of a laser tracking measurement system is met.

Description

Technical Field

[0001] The utility model relates to the technical field of dense bead shaft systems, in particular to a dense bead shaft system used in a laser tracking measurement system. Background Art

[0002] The dense bead shaft system is based on the error averaging effect of dense steel balls, which can significantly reduce the impact of part manufacturing errors on shaft accuracy and improve the geometric accuracy of rotary shafts. It is widely used in precision instrument spindles, turntables, and machine tool spindles. However, the laser tracking measurement system has high requirements for the rotation accuracy of the dense bead shaft system, and the existing dense bead shaft system cannot meet the rotation accuracy requirements of the laser tracking measurement system. Utility Model Content

[0003] Aiming at the technical problem that the existing dense bead shaft system cannot meet the rotation accuracy requirement of the laser tracking measurement system; the utility model provides a dense bead shaft system for the laser tracking measurement system, which has high rotation accuracy and meets the rotation accuracy requirement of the laser tracking measurement system.

[0004] The utility model is realized by the following technical solutions:

[0005] The utility model provides a dense bead shaft system for a laser tracking measurement system, comprising: a main shaft, one end of which is provided with a limited position boss; a radial retaining frame, which is equipped with a plurality of radial steel balls and is sleeved outside the main shaft; a first thrust frame, which is equipped with a plurality of end face steel balls and is sleeved outside the main shaft; a second thrust frame, which is equipped with a plurality of supporting steel balls and is sleeved outside the main shaft; wherein the first thrust frame and the second thrust frame are respectively located outside the corresponding ends of the radial retaining frame.

[0006] The utility model provides a dense ball shaft system for a laser tracking and measuring system, wherein a limiting boss is arranged at one end of a main shaft and a radial retainer is sleeved thereon, wherein a plurality of radial steel balls are installed on the radial retainer to cooperate with the shaft sleeve to form a radial dense ball bearing, and a first thrust frame and a second thrust frame are respectively provided at both ends of the radial retainer, wherein a plurality of end face steel balls are installed on the first thrust frame to cooperate with the limiting boss and corresponding mounting components to form a first thrust dense ball bearing, and a plurality of supporting steel balls are installed on the second thrust frame to cooperate with corresponding mounting components to form a second thrust dense ball bearing, and the first thrust bearing, the radial dense ball bearing and the second thrust bearing form an I-shaped structure, thereby reducing the radial and axial motion errors of the dense ball shaft system and improving the bearing capacity of the shaft system. Therefore, the utility model has high rotation accuracy and meets the rotation accuracy requirement of the laser tracking and measuring system.

[0007] In an optional embodiment, it also includes a sleeve, which is arranged outside the radial retaining frame, and the two end faces of the sleeve are in contact with the corresponding end face steel balls and the supporting steel balls, so that the sleeve serves as the outer ring of the radial bearing and the inner ring of the thrust bearing at the same time, which can simplify the structure of the shaft system and thus improve the reliability and rotation accuracy of the shaft system.

[0008] In an optional embodiment, the sleeve, the main shaft and the radial steel balls are interference fit to control the friction torque.

[0009] In an optional embodiment, the interference between the sleeve, the main shaft and the radial steel ball is 3.82 to 8 microns.

[0010] In an optional embodiment, a pressure ring is further included, which is sleeved outside the main shaft and can press the supporting steel ball onto the corresponding end surface of the sleeve to facilitate fixing the first thrust frame and the second thrust frame outside the main shaft.

[0011] In an optional embodiment, it also includes a locking nut, which is threaded on the end of the main shaft away from the limiting boss, and an elastic gasket is arranged between the locking nut and the pressure ring, so that the shaft system can be fixed through the cooperation of the locking nut and the elastic gasket, and the shaft system preload force can be adjusted to reduce the influence of temperature changes on the rotation accuracy of the shaft system.

[0012] In an optional embodiment, the elastic gasket is a disc spring.

[0013] In an optional embodiment, the radial steel balls are arranged in a multi-start spiral on the radial retaining frame so that the radial raceways of the steel balls do not overlap each other and maintain symmetry in the diameter direction, which is beneficial to reducing radial bearing wear and increasing the service life of the radial bearing.

[0014] In an optional embodiment, the diameters of the radial steel balls, the end steel balls and the supporting steel balls are all 6.35 mm to ensure that the performance parameters of the dense ball shaft system meet the design requirements.

[0015] In an optional embodiment, the main shaft is a hollow structure to facilitate the insertion of the transverse axis and optical module cables.

[0016] Compared with the prior art, the utility model has the following advantages and beneficial effects:

[0017] The utility model provides a dense ball shaft system for a laser tracking and measuring system, wherein a limiting boss is arranged at one end of a main shaft and a radial retainer is sleeved thereon, wherein a plurality of radial steel balls are installed on the radial retainer to cooperate with the shaft sleeve to form a radial dense ball bearing, and a first thrust frame and a second thrust frame are respectively provided at both ends of the radial retainer, wherein a plurality of end face steel balls are installed on the first thrust frame to cooperate with the limiting boss and corresponding mounting components to form a first thrust dense ball bearing, and a plurality of supporting steel balls are installed on the second thrust frame to cooperate with corresponding mounting components to form a second thrust dense ball bearing, and the first thrust bearing, the radial dense ball bearing and the second thrust bearing form an I-shaped structure, thereby reducing the radial and axial motion errors of the dense ball shaft system and improving the bearing capacity of the shaft system. Therefore, the utility model has high rotation accuracy and meets the rotation accuracy requirement of the laser tracking and measuring system. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required for use in the embodiments will be briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present application and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without paying creative work.

[0019] In the attached picture:

[0020] Figure 1 This is a schematic diagram of the structure of a dense bead shaft system used in a laser tracking measurement system according to an embodiment of the utility model;

[0021] Figure 2 This is a schematic structural diagram of a radial retainer according to an embodiment of the utility model;

[0022] Figure 3 This is a schematic structural diagram of a first thrust frame according to an embodiment of the utility model;

[0023] Figure 4 It is a schematic structural diagram of the second thrust frame of the embodiment of the utility model.

[0024] Marks and corresponding parts names in the attached drawings:

[0025] 1-spindle, 2-limiting boss, 3-radial retainer, 4-first thrust frame, 5-end face steel ball, 6-second thrust frame, 7-support steel ball, 8-sleeve, 9-pressure ring, 10-locking nut, 11-elastic gasket. DETAILED DESCRIPTION

[0026] In order to make the purpose, technical solution and advantages of the embodiments of the present application clearer, the technical solution in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, not all of the embodiments. It should be noted that similar reference numerals and letters represent similar items in the following drawings, so once an item is defined in one drawing, it does not need to be further defined and explained in the subsequent drawings.

[0027] In the description of the embodiments of the present application, the indicated orientation or position relationship is based on the orientation or position relationship shown in the accompanying drawings, or is the orientation or position relationship in which the product of the application is conventionally placed when in use, or is the orientation or position relationship conventionally understood by those skilled in the art. It is only for the convenience of describing the present application and simplifying the description, and does not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present application.

[0028] In the description of the present invention, unless otherwise clearly specified and limited, the terms "disposed", "opened", "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection, a direct connection, or an indirect connection through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0029] Example:

[0030] Combination Figure 1-Figure 4 The present embodiment provides a dense bead shaft system for a laser tracking measurement system, comprising: a main shaft 1, one end of which is provided with a limited boss 2; a radial retainer 3, which is equipped with a plurality of radial steel balls and is sleeved outside the main shaft 1; a first thrust frame 4, which is equipped with a plurality of end face steel balls 5 and is sleeved outside the main shaft 1; a second thrust frame 6, which is equipped with a plurality of supporting steel balls 7 and is sleeved outside the main shaft 1; wherein the first thrust frame 4 and the second thrust frame 6 are respectively located outside the corresponding ends of the radial retainer 3.

[0031] Specifically, the present embodiment further comprises a sleeve 8 and a pressure ring 9, wherein the sleeve 8 is sleeved outside the radial retainer 3, and the two end faces of the sleeve 8 are in contact with the corresponding end face steel balls 5 and the supporting steel balls 7, and the pressure ring 9 is sleeved outside the main shaft 1, and the pressure ring 9 can press the supporting steel balls 7 onto the corresponding end faces of the sleeve 8, so as to facilitate fixing the first thrust frame 4 and the second thrust frame 6 outside the main shaft 1. The sleeve 8 can simultaneously serve as the outer ring of the radial bearing and the inner ring of the thrust bearing, which can simplify the structure of the shaft system, thereby improving the reliability and rotation accuracy of the shaft system. That is to say, the main shaft 1, the radial retainer 3, the radial steel balls and the sleeve 8 constitute a radial dense ball bearing; the limiting boss 2, the first thrust frame 4, the end face steel balls 5 and the sleeve 8 constitute a first thrust dense ball bearing (upper thrust dense ball bearing); the pressure ring 9, the second thrust frame 6, the supporting steel balls 7 and the sleeve 8 constitute a second thrust dense ball bearing (lower thrust dense ball bearing).

[0032] In this embodiment, the sleeve 8, the spindle 1 and the radial steel ball are interference fit to control the friction torque. Specifically, the interference fit between the sleeve 8, the spindle 1 and the radial steel ball is 3.82 to 8 microns.

[0033] The diameters of the radial steel balls, the end steel balls 5 and the support steel balls 7 are all 6.35 mm to ensure that the performance parameters of the dense bead shaft system meet the design requirements.

[0034] Combination Figure 2 The radial steel balls are arranged in a multi-start spiral on the radial retainer 3, so that the radial raceways of the steel balls do not overlap each other and maintain symmetry in the diameter direction, which is beneficial to reducing radial bearing wear and increasing the service life of the radial bearing.

[0035] On this basis, this embodiment also includes a locking nut 10, which is threaded on the end of the main shaft 1 away from the limiting boss 2, and an elastic gasket 11 is arranged between the locking nut 10 and the pressure ring 9, so that the shaft system can be fixed through the cooperation of the locking nut 10 and the elastic gasket 11, and the shaft system preload can be adjusted to reduce the influence of temperature changes on the rotation accuracy of the shaft system.

[0036] Preferably, the elastic gasket 11 is a disc spring.

[0037] In addition, the main shaft 1 is a hollow structure, so as to facilitate the insertion of the transverse axis and the optical module cables.

[0038] In summary, the present embodiment provides a close-coupled bead shaft system for a laser tracking measurement system, wherein a limiting boss 2 is provided at one end of a main shaft 1, and a radial retainer 3 is sleeved thereon, wherein the radial retainer 3 is provided with a plurality of radial steel balls, and the main shaft 1, the radial retainer 3, the radial steel balls and the shaft sleeve 8 constitute a radial close-coupled bead bearing, and a first thrust frame 4 and a second thrust frame 6 are provided at both ends of the radial retainer 3, wherein the first thrust frame 4 is provided with a plurality of end face steel balls 5, so that the limiting boss 2, the first thrust frame 4, the end face steel balls 5 and the shaft sleeve 8 constitute a first thrust close-coupled bead bearing (upper thrust close-coupled bead bearing); the second thrust frame 6 is provided with a plurality of supporting steel balls 7, so that a pressure ring 9, the second thrust frame 6, the supporting steel balls 7 and the shaft sleeve 8 constitute a second thrust close-coupled bead bearing (lower thrust close-coupled bead bearing), and the first thrust bearing, the radial close-coupled bead bearing and the second thrust bearing form an I-shaped structure, thereby reducing the radial and axial motion errors of the close-coupled bead shaft system and improving the bearing capacity of the shaft system.

[0039] To facilitate understanding of the beneficial technical effects of this embodiment, this embodiment is described by taking the use requirements of the dense bead shaft system with radial and axial motion errors better than 1 μm and a load capacity greater than 25 kg as an example, specifically:

[0040] In the embodiment, the radial ball bearing adopts the basic hole system, so the journal size of the main shaft 1 needs to be matched according to the radial steel ball size, the sleeve 8 size and the corresponding interference. For example, a steel ball with a diameter of Sφ6.35mm is selected, and the main shaft 1 is hollow, and its inner hole diameter is φ30mm, which can allow the transverse axis and the optical module cable to pass through. The motor is initially selected to set the journal size of the main shaft 1 to be twice the inner hole diameter, that is, set to φ60mm. According to the estimation of the shaft system itself and the external load of 25kg, its moment of inertia J is 106648.32kg / mm2, the shaft system speed range is estimated to be (0-180° / s) or (0-30r / min), and the estimated acceleration a range is (360° / s2, angular acceleration is 6.28rad / s2), then the maximum rotation torque is:

[0041] M=Jα≈0.67N·m

[0042] At the same time, spindle 1 is a hollow shaft with an inner diameter of 30mm and an outer diameter of 60mm. The material is GCr15 and its allowable torsional stress is 50MPa. Therefore, it can be calculated:

[0043]

[0044] Where: d is the shaft diameter at the cross section; T is the torque transmitted by the shaft; [τ] is the allowable torsional stress of the shaft; and v is the ratio of the inner diameter to the outer diameter of the hollow shaft.

[0045] The stiffness calculation for spindle 1 is as follows:

[0046] The spindle 1 is prone to torsional deformation under load, and high-precision instruments have high requirements for torsional deformation, so it is necessary to check the stiffness of the spindle 1. The torsional deformation of the shaft is usually expressed in terms of the torsional angle per meter of shaft length. The calculation formula for the torsion angle of the hollow optical axis is:

[0047]

[0048]

[0049] Among them: l is the length of the shaft subjected to torque; G is the shear modulus of the shaft; d is the outer diameter of the main shaft; d0 is the inner diameter of the main shaft.

[0050] From this, it can be seen that the spindle meets the requirement of precision transmission shaft for torsional deformation not exceeding 0.25° / m.

[0051] The roughness of spindle 1 is as follows:

[0052] The surface roughness of spindle 1 mainly affects the service life of the bearing. The roughness value is generally selected between 0.032 and 0.08 μm. If it is too smooth, it is not conducive to bearing lubrication. The roughness of the important surface of spindle 1 is selected according to the recommended surface roughness value of the important surface of the P2 grade angular contact bearing ring and related literature, and the surface roughness is corrected according to the actual processing capacity, as shown in Table 1.

[0053] Serial number Important surfaces Dimensions / mm Roughness / μm 1 Journal φ60 0.1(0.050 recommended value) 2 Shaft end face φ60~φ128 0.1(0.050 recommended value)

[0054] Table 1

[0055] Spindle 1 shape and position tolerance:

[0056] The important surfaces of spindle 1 are the upper end face and the spindle diameter, and the main geometric error items are the perpendicularity of the end face to the axis, and the roundness and cylindricity of the journal of spindle 1. According to the actual processing capacity, the geometric tolerance design of each main surface is shown in Table 2.

[0057]

[0058] Table 2

[0059] For the basic structure of the sleeve 8:

[0060] Since the radial ball bearing adopts the basic hole system, the journal size of the main shaft 1 needs to be matched according to the radial steel ball size, the 8-inch sleeve and the corresponding interference. Since the radial steel ball diameter is 6.35mm and the main shaft 1 journal is φ60mm, the inner diameter size of the sleeve 8 is φ72.7mm, and the H7 tolerance is selected.

[0061] The surface roughness of the sleeve 8 mainly affects the service life of the bearing, and is generally selected between 0.032 and 0.08 μm. Too smooth a sleeve 8 is not conducive to bearing lubrication. The roughness of the important surface of the sleeve 8 is selected according to the recommended surface roughness value of the important surface of the P2 grade angular contact bearing ring and related literature, and the surface roughness is corrected according to the actual processing capacity, as shown in Table 3.

[0062] Serial number Important surfaces Dimensions / mm Roughness / μm 1 Bushing inner hole φ72.7 0.1(0.050 recommended value) 2 Upper and lower end faces of sleeve φ72.7~φ128 0.1(0.050 recommended value)

[0063] Table 3

[0064] The important surfaces of the sleeve 8 are the upper end face, the lower end face and the inner hole of the sleeve 8. The main geometric error items are the perpendicularity of the end face to the axis, the roundness and cylindricity of the inner hole of the sleeve 8. According to the actual processing capacity, the geometric tolerance design of each main surface of the sleeve 8 is shown in Table 4.

[0065]

[0066] Table 4

[0067] For radial balls:

[0068] The radial steel balls shall meet the requirements of standard GB / T 308.1-2013. In this embodiment, the ball batch is selected as G5 grade steel balls, the ball diameter is Sφ6.35mm, and the diameter variation of the ball batch is 0.25μm. Since the diameter variation requirements of the ball batch and the single ball are inconsistent, further refinement is still required to control the diameter variation between single balls within 0.25μm. The surface roughness of the ball batch is still consistent with the requirements of the single ball, with a spherical error of 0.13μm and a surface roughness of 0.014μm.

[0069] In addition, the radial interference should at least eliminate the geometric errors and surface roughness of the radial steel ball, sleeve 8 and the journal of the spindle 1. The following formula can be used to calculate that the interference should be greater than 3.82μm. The radial interference is preliminarily determined to be 4 to 8μm. It is still necessary to test the parts after they are processed and accurately calculate the interference.

[0070] Δ gy >(Δ Z1 +Δ Z2 +2Δ Z3 )+(Δ T1 +Δ T2 +2Δ T3 )+(2Δ Q1 +2Δ Q2 +4Δ Q3 )

[0071] Wherein: Δgy is the radial interference; ΔZ1, ΔT1 and ΔQ1 are the roundness errors of spindle 1, sleeve 8 and the diameter variation of radial steel ball respectively; ΔZ2, ΔT2 and ΔQ2 are the cylindricity errors of spindle 1, sleeve 8 and the spherical error of radial steel ball respectively; ΔZ3, ΔT3 and ΔQ3 are the surface roughness of spindle 1, sleeve 8 and radial steel ball respectively.

[0072] Calculation of allowable interference of radial ball bearing size:

[0073] The main parameters of radial dense ball bearings are: outer ring inner diameter 72.7mm, inner ring outer diameter 60mm, ball diameter 6.35mm, material GCr15, hardened HRC62~65, Poisson's ratio υ=0.3, elastic modulus E=2×105N / mm2. The radial steel ball does not bear radial external load except for the interference. The radial dense ball bearing does not bear external load and runs at low speed.

[0074] Therefore, according to calculation, the maximum allowable interference is 18.7μm, and the set interference is 4 to 8μm, so it is within the allowable range.

[0075] It should be noted that the calculation of the interference of the axial ball bearing (the first thrust ball bearing and the second thrust ball bearing) is as follows:

[0076] The axial interference size should eliminate the influence of the shape and position error of the sleeve 8, the shape and position error of the spindle 1, the shape and position error of the pressure plate 9 and the surface roughness. According to the following formula, the axial interference should be greater than 5.22μm, and the initial axial interference is 5.5-8μm. In the actual process, it is necessary to measure the influence of the interference on the friction torque and determine the optimal interference.

[0077] Δ zgy >2(Δ ZZ1 +Δ ZZ2 )+2(Δ TZ1 +Δ TZ2 )+(2Δ QZ1 +2Δ QZ2 +4Δ QZ3 )

[0078] Wherein: Δzgy is the axial interference; ΔZZ1, ΔTZ1 and ΔQZ1 are the verticality errors of the main shaft 1, the sleeve 8 and the diameter changes of the end steel ball 5 / support steel ball 6 respectively; ΔZ2, ΔT2 and ΔQ2 are the roughness of the main shaft 1, the sleeve 8 and the spherical errors of the end steel ball 5 / support steel ball 6; ΔQZ3 is the surface roughness of the end steel ball 5 / support steel ball 6.

[0079] Calculation of allowable interference of axial ball bearing size:

[0080] The steel balls used in the axial ball bearings are of the same size as the radial balls. Since the axial ball bearings bear their own weight and the load on top, totaling 30kg, the load on the bottom reduces the influence of the interference on the contact strength. According to calculations, the maximum allowable interference is 18.6μm.

[0081] About the influence of temperature on the interference of ball bearings:

[0082] Since the steel ball, 1 sleeve and main shaft 8 are made of the same material, that is, bearing steel, their linear expansion coefficients are the same. When the bearing is heated evenly during operation, the temperature has little effect on the radial interference and can still operate within the normal range.

[0083] However, for thrust ball bearings, thermal deformation causes axial elongation of the bearing, reducing the axial locking force, especially the heat of the motor is directly transmitted to the spindle 1, reducing the axial interference, so special attention should be paid. At the same time, the temperature and accuracy can be tested during the temperature rise test.

[0084] About radial cage 3:

[0085] The design of the radial retainer 3 mainly considers the arrangement of radial steel balls, and usually adopts a multi-start spiral arrangement so that the raceways do not overlap each other and maintain symmetry in the diameter direction, which is beneficial to reducing bearing wear and increasing bearing service life. In this embodiment, the radial retainer 3 is a solid retainer, and the material selected is H62. It can be processed according to the cast copper and copper alloy specified in the JB / T 11841-2014 standard (tin bronze alloy).

[0086] Combination Figure 2 The center position of the radial cage 3 hole is determined by two parameters: the distance from the end face and the angle from the starting hole in the cylindrical coordinate system. There are 144 holes on the cylindrical surface of the radial cage 3, which are arranged in a spiral line in four quadrants, equivalent to a four-start spiral line, that is, the number of heads is 4. There are four symmetrically distributed balls in the diameter direction, and the angle between two adjacent center lines is 15°.

[0087] In order to prevent the four steel ball raceways from overlapping in the diameter direction, the four steel balls in adjacent quadrants should be staggered axially by a small distance Δ. In this embodiment, Δ is taken as 0.45 mm, which is converted into an axial distance interval increment k=0.45×Δ=1.8 mm for adjacent balls on the same spiral line. At the same time, to ensure that the four spiral lines are in different axial positions on the same section, they are staggered by a small angle, which is 15° / 4=3.75°.

[0088] About the first thrust frame 4:

[0089] Combination Figure 3The first thrust frame 4 is mainly used for the axial bearing of the dense ball shaft system. Appropriate density can improve the bearing capacity and axial rotation accuracy of the shaft system. In this embodiment, the first thrust frame 4 uses two rows of dense holes, and the position of each hole is determined by the angle from the starting hole and the radius from the center of the cage. If the first thrust frame 4 has a total of 48 holes, the center line angle of each row of adjacent holes is 15°. Take the spacing value Δ as 0.3mm, then the incremental coefficient k of the spacing of each row of balls in each quadrant is k=4×Δ=1.2mm.

[0090] About the second thrust frame 6:

[0091] Combination Figure 4 The second thrust frame 6 is similar to the first thrust frame 4, except that the second thrust frame 6 has 24 holes in a row, and the centerline angle of each row of adjacent holes is 18°. The second thrust frame 6 takes the spacing value Δ as 0.4mm, and the spacing increment coefficient is set to 2mm. The second thrust frame 6 is used to install the support steel balls to prevent the bearing from overturning, so the number of steel balls can be reduced.

[0092] Press ring 9:

[0093] The pressure ring 9, the main shaft 1, the supporting steel ball 7 and the sleeve 8 together form the lower thrust ball bearing. The flatness and surface roughness of the pressure ring 9 have a great influence on the axial rotation accuracy of the bearing, so it needs to be strictly controlled. The specific parameters are shown in Table 5.

[0094] Serial number Important surfaces Dimensions / mm Roughness / μm Flatness / μm 1 Lower thrust surface Φ100 0.05 0.5

[0095] Table 5

[0096] Regarding lock nut 10:

[0097] The locking nut 10 is mainly used to provide sufficient axial locking force to ensure the axial interference and bearing capacity of the thrust ball bearing of the shaft system. The size of the locking force directly affects the friction torque and axial rotation accuracy of the shaft system. How to achieve uniform application of the locking force on the pressure ring 9 is the key. In this embodiment, the locking nut 10 and the disc spring are used to achieve the axial locking force on the pressure ring 9. In addition, the locking can be achieved by using an adjustment piece in combination with a double nut. By calculating the size chain and grinding the adjustment piece, the locking force can be tightened to achieve the specified interference. The size of the axial locking force is achieved by adjusting the locking nut according to the axial interference, and the friction torque of the shaft system rotation is reduced by measuring and adjusting at the same time.

[0098] If the thrust bearing is subjected to external force and load of 300N, the force on a single steel ball is:

[0099]

[0100] The elastic deformation caused is:

[0101]

[0102] In the formula, R is the radius of the steel ball; ν1 is the Poisson's ratio of the steel ball; ν2 is the Poisson's ratio of the upper thrust plate; E1 is the elastic modulus of the steel ball; E2 is the elastic modulus of the upper thrust plate. Among them, E1=E2=2.08×105N / mm2; ν1=ν2=0.3.

[0103] but:

[0104]

[0105] Therefore, the axial interference needs to be corrected to 6μm to 8μm. In the actual assembly process, fine-tuning between 5μm and 6μm is still required.

[0106] Calculation of locking force of locking nut 10:

[0107] To eliminate the shape and position errors of the beaded shaft system, it is necessary to ensure that the axial interference is set as the preload of the bearing. Since the minimum interference is set to 6μm, the number of upper and lower thrust bearings is inconsistent, the interference of the upper thrust bearing is 1.16μm, and the interference of the lower thrust bearing is 1.84μm. It can be calculated that the force of a single steel ball is about 8N, and the preload of the bearing can be obtained to be about: 200N. When the maximum interference is 8μm, the force of the steel ball is about 12N, and the preload is about 270N.

[0108] The locking torque of the shaft locking nut 10 is the sum of the thread friction torque T1 and the support surface friction torque T2. The calculation formula for the tightening torque of the nut is:

[0109]

[0110] In the formula, F is the preload force; d2 is the thread diameter, λ is the thread lead angle, and the calculation formula is:

[0111] ρv is the equivalent friction angle of the thread, ρv=arctan(μs), μs is the friction coefficient of the nut contact surface; dm is the equivalent diameter of the nut support surface, which is half of the sum of the minimum contact diameter and the maximum contact diameter; f1 is the friction coefficient of the nut support surface.

[0112] According to the above formula, it can be calculated that the tightening torque is 2N·m~2.5N·m.

[0113] About the friction torque of radial ball bearings:

[0114] According to the empirical formula of friction torque, we can get:

[0115]

[0116]

[0117] Among them: is the positive pressure borne by a single ball, including external load and interference load; Dr is the equivalent diameter of the ball bearing; f is the friction coefficient, take f = 0.001; K1 considers the influence of lubricating material on the bearing friction torque; K2 considers the influence of isolation ring structure and assembly quality on bearing friction; K3 considers the influence of temperature on bearing friction torque.

[0118] About the friction torque of thrust ball bearing:

[0119] For the upper thrust ball bearing (first thrust ball bearing), the empirical formula for the friction torque can be obtained as follows:

[0120]

[0121]

[0122] Among them: is the positive pressure borne by a single ball, including external load and interference load; Dr is the equivalent diameter of the ball bearing; f is the friction coefficient, take f = 0.001; K1 considers the influence of lubricating material on the bearing friction torque; K2 considers the influence of isolation ring structure and assembly quality on bearing friction; K3 considers the influence of temperature on bearing friction torque.

[0123] The friction torque of the lower thrust ball bearing (second thrust ball bearing) is about half of that of the upper thrust bearing, which can be taken as 76.70 N·mm.

[0124] Total friction torque estimation:

[0125] The total friction torque is 0.5 N·m.

[0126] In addition, the error averaging effect of the bead-type shaft system has not been explored, and the tolerance design of the main components and the selection of the assembly interference are still based on empirical formulas and references. In addition, due to the sharp increase in the friction torque of the shaft system caused by the selection of the interference and the bearing preload, the prediction of the friction torque is also based on empirical formulas, and it is not clear whether the selection of motors can meet the requirements. In addition, the influence of torque fluctuations and speed fluctuations on the rotation accuracy of the shaft system is still unclear. Therefore, it is necessary to carry out the following experiments.

[0127] Geometric accuracy of the rotation axis:

[0128] The test method is as follows: the geometric accuracy of the rotary axis of the bead-type shaft system is tested according to the geometric accuracy of the rotary axis of GB / T 17421.7-2015. A standard ball is placed on the upper end of the bead-type shaft system provided in this embodiment, and the eccentricity between the standard ball and the axis of the bead-type shaft system is adjusted to the minimum using a sensor. Then, the radial error motion and axial error motion of the bead-type shaft system are tested.

[0129] The influence of different bearing parts configuration on rotation accuracy:

[0130] Disc springs, high-precision plates and high-precision locking nuts are used respectively to achieve axial locking of the ball bearing. The axial locking methods of high-precision plates, flat springs, pressure plates and high-precision locking nuts are compared to select the better axial locking method.

[0131] Shafting temperature rise and thermal deformation test:

[0132] The shaft system moves at a low speed, the speed is set to 30r / min, and the absolute temperature limit is determined to be 50°C. Start working at a starting speed of 30r / min. Monitor the temperature rise at the sleeve position until the temperature stabilizes. If the temperature reaches the limit, stop running and let the bearing cool. Repeat this process at the same speed, allowing the spindle to run until the temperature stabilizes below the limit. Once the bearing temperature stabilizes, continue to run the spindle for 10-15 minutes. Then, increase the speed by a certain increment and repeat step 4. Continue to increase the speed incrementally, keeping the temperature stable at each stage until the spindle reaches a speed range higher than the system operating speed. Carry out a dense bead shaft system thermal deformation test in accordance with GB / T 17421.3-2009, and use a high-precision double standard ball to monitor the thermal deformation of the spindle.

[0133] Experiment on angle measurement accuracy and speed uniformity of dense bead shaft system:

[0134] Based on the principle of multi-reading head averaging, we conduct research on high-precision angle measurement technology; based on high-precision time reference, we conduct research on rate accuracy and rate stability. We conduct verification and compensation tests on shaft system angle measurement accuracy based on multi-tooth indexing table, autocollimator and laser interferometer.

[0135] Experiment on friction starting torque of dense bead shaft system and torque fluctuation after starting:

[0136] Firstly, steel wire and dynamometer are used to preliminarily determine the friction aerodynamic torque of the bearing to verify whether the selected click can drive the bead-type shaft system. Then, a bead-type shaft system friction starting torque detection test bench is built and monitored using a high-precision torque sensor to determine the friction starting torque of the bead-type shaft system and the torque fluctuation after the speed stabilizes.

[0137] Ball and cage assembly:

[0138] Since the steel ball installation method of the ball hole is difficult to process, a stepped hole method is used. The taper angle of the small end of the hole is 90°, and the gap between the steel ball and the ball hole is 0.1mm. The steel ball is placed in the ball hole, and riveted at the large end of the ball hole to seal the steel ball in the ball hole.

[0139] It should be noted that due to the use of straight cylindrical holes for riveting, the range of movement of the steel ball in the cage ball hole will be increased, and it is easy for the bottom surface of the cage or the outer cylindrical surface to rub against the outer surface of the sleeve. Therefore, special attention should be paid to the control of the cage thickness and the movement of the steel ball. If friction is unavoidable during processing, four steel balls can be symmetrically distributed on the edge of the cage to support the cage and avoid friction.

[0140] At the same time, since there is a small interference between the spindle 1, the sleeve 8 and the steel ball, the interference is selected to be 0.004-0.008mm. Usually, the vertical shaft cage is screwed into the sleeve 8 by rotating, but it is easy to damage the surface of the spindle 1 and the sleeve 8, so the thermal installation method is adopted:

[0141] Heat the shaft 8 to a temperature difference of 35℃ with the spindle 1, and the clearance is about 0.015mm. In the actual process, it should be 20℃ higher than this temperature difference. If assembled at an ambient temperature of 20℃, the heating temperature of the sleeve 8 is 70℃. The assembly process should be quick, and the steel ball should not collide with the sleeve and other parts until the steel ball of the thrust bearing contacts the upper end face of the sleeve; the radial cage should have a certain clearance of about 0.1mm or more with the end face of the spindle.

[0142] For installation of axial locking parts:

[0143] Install the lower thrust part on the vertical shaft, install the high-precision thrust plate (pressure ring 9), disc spring (elastic gasket 11) and lock nut 10, use a hook spanner to tighten the lock nut 10, and rotate it 45°; use a torque spanner to tighten the bearing lock nut 10, and the tightening torque is 2.5N·m. This tightening torque is adjusted by detecting the friction torque and rotation accuracy.

[0144] Therefore, it is verified that this embodiment meets the requirement that the torsional deformation of the precision transmission shaft is not greater than 0.25° / m, and meets the stiffness requirement of the shaft.

[0145] In summary, the dense bead shaft system provided in this embodiment has high rotation accuracy and meets the rotation accuracy requirements of the laser tracking measurement system.

[0146] The specific implementation methods described above further illustrate the purpose, technical solutions and beneficial effects of the utility model in detail. It should be understood that the above description is only the specific implementation method of the utility model and is not used to limit the protection scope of the utility model. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the utility model should be included in the protection scope of the utility model.

Claims

1. A dense bead axis system for a laser tracking measurement system, characterized in that: include: A main shaft (1) is provided with a limiting boss (2) at one end; A radial retainer (3) mounted with a plurality of radial steel balls and sleeved outside the main shaft (1); A first thrust frame (4) is provided with a plurality of end surface steel balls (5) and is sleeved outside the main shaft (1); A second thrust frame (6) is provided with a plurality of supporting steel balls (7) and is sleeved outside the main shaft (1); The first thrust frame (4) and the second thrust frame (6) are respectively located outside corresponding ends of the radial retaining frame (3).

2. The dense bead shaft system for laser tracking measurement system according to claim 1, characterized in that: It also comprises a shaft sleeve (8), which is sleeved outside the radial retaining frame (3), and the two end surfaces of the shaft sleeve (8) abut against the corresponding end surface steel balls (5) and the supporting steel balls (7).

3. The dense bead shaft system for laser tracking measurement system according to claim 2, characterized in that: The shaft sleeve (8), the main shaft (1) and the radial steel ball are interference fit.

4. The dense bead shaft system for laser tracking measurement system according to claim 3, characterized in that: The interference between the shaft sleeve (8), the main shaft (1) and the radial steel ball is 3.82 to 8 microns.

5. The dense bead shaft system for laser tracking measurement system according to claim 2, characterized in that: It also includes a pressure ring (9), which is sleeved outside the main shaft (1), and the pressure ring (9) can press the supporting steel ball (7) onto the corresponding end surface of the shaft sleeve (8).

6. The dense bead shaft system for laser tracking measurement system according to claim 5, characterized in that: It also comprises a locking nut (10), wherein the locking nut (10) is threadedly connected to an end of the main shaft (1) away from the limiting boss (2), and an elastic gasket (11) is arranged between the locking nut (10) and the pressure ring (9).

7. The dense bead shaft system for laser tracking measurement system according to claim 6, characterized in that: The elastic gasket (11) is a disc spring.

8. The dense bead shaft system for laser tracking measurement system according to claim 1, characterized in that: The radial steel balls are arranged on the radial retaining frame (3) in the form of a multi-start helix.

9. The dense bead shaft system for a laser tracking measurement system according to any one of claims 1 to 8, characterized in that: The diameters of the radial steel balls, the end surface steel balls (5) and the supporting steel balls (7) are all 6.35 mm.

10. The dense bead shaft system for laser tracking measurement system according to any one of claims 1 to 8, characterized in that: The main shaft (1) is a hollow structure.

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