Bearing device and bearing system

Abstract

To provide a bearing device that inhibits frictional torque caused in itself from increasing and has a long life.SOLUTION: A bearing device 31 includes: a first rolling bearing 33 in which a first inner ring 43 and a first outer ring 44 are connected via a first rolling element 45; a second rolling bearing 34 in which a second inner ring 48 and a second outer ring 49 are connected via a second rolling element 50; and a first connection member 32 connected to the first outer ring 44 and the second inner ring 48 respectively.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a bearing device and a bearing system. [Background technology]

[0002] Conventionally, a ball bearing (rolling bearing; bearing device) has been used to support a shaft portion (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2020-162245 A Summary of the Invention [Problem to be solved by the invention]

[0004] A ball bearing is configured by connecting an inner ring and an outer ring via rolling elements. However, when the sliding surfaces between the inner and outer rings and the rolling elements become worn, the friction torque generated in the ball bearing increases, shortening the life of the ball bearing.

[0005] The present invention has been made in consideration of these problems, and has an object to provide a long-life bearing device that suppresses the increase in friction torque generated within the device, and a bearing system equipped with this bearing device. [Means for solving the problem]

[0006] In order to solve the above problems, the present invention proposes the following means. The bearing device of the present invention is characterized by comprising a first rolling bearing in which a first inner ring and a first outer ring are connected via a first rolling element, a second rolling bearing in which a second inner ring and a second outer ring are connected via a second rolling element, and a first connecting member fixed to each of the first outer ring and the second inner ring.

[0007] According to the invention, in the first rolling bearing, the first rolling element rolls between the first inner ring and the first outer ring, and in the second rolling bearing, the second rolling element rolls between the second inner ring and the second outer ring. For example, the shaft portion is fixed to the first inner ring of the first rolling bearing so as to be coaxial with the first rolling bearing. The second outer ring of the second rolling bearing is supported. For example, when a first friction torque generated between the first inner ring and the first outer ring via the first rolling element is smaller than a second friction torque generated between the second inner ring and the second outer ring via the second rolling element, the second rolling bearing stops, and the shaft portion and the first inner ring rotate together around the axis of the first rolling bearing relative to the first outer ring, the first connecting member, and the second rolling bearing. When the first friction torque becomes larger than the second friction torque, the first rolling bearing stops, and the shaft portion, the first rolling bearing, the first connecting member, and the second inner ring rotate together around the axis of the second outer ring. In this way, even if the first rolling bearing stops, the shaft portion can be rotated about the axis by the second rolling bearing. Therefore, compared to a bearing device equipped with only one rolling bearing, the friction torque generated in the bearing device is prevented from increasing, and the bearing device can have a longer life.

[0008] In the bearing device, the first rolling bearing and the second rolling bearing may be coaxial with each other and arranged side by side along the axial direction of the first rolling bearing. According to this invention, it is possible to prevent the outer diameter of the bearing device in the direction perpendicular to the axis from becoming large.

[0009] In the bearing device, the first rolling bearing and the second rolling bearing may have the same inner diameter and the same outer diameter. According to this invention, the first friction torque of the first rolling bearing and the second friction torque of the second rolling bearing can be easily made equal to each other. Therefore, the magnitude relationship between the two friction torques can be easily switched between a state in which the first rolling bearing is operating and the second rolling bearing is stationary and a state in which the first rolling bearing is stationary and the second rolling bearing is operating.

[0010] In the bearing device, the first connecting member may have a shape that is rotationally symmetric about the axis of the first rolling bearing. According to this invention, when the first connecting member rotates about the axis, the movement of the first connecting member can be stabilized, and therefore the movement of each of the first rolling bearing and the second rolling bearing fixed to the first connecting member about the axis can be stabilized.

[0011] In addition, in the bearing device, the first connecting member may have a first cylindrical member fixed to the second inner ring, a second cylindrical member fixed to the first outer ring, and an annular member connecting the axial end of the first rolling bearing in the first cylindrical member and the axial end of the second cylindrical member. According to this invention, the first connecting member can be easily formed from three members, namely, the first tubular member, the second tubular member, and the annular member.

[0012] Furthermore, in the bearing device, when friction torque generated between the first inner ring and the first outer ring via the first rolling element is defined as first friction torque, and friction torque generated between the second inner ring and the second outer ring via the second rolling element is defined as second friction torque, the bearing device may be configured to switch from a state in which the first friction torque is smaller than the second friction torque, the second rolling bearing is stopped, and a plurality of first sliding surfaces between the first inner ring and the first outer ring and the first rolling element slide against each other, to a state in which the first friction torque is larger than the second friction torque, the first rolling bearing is stopped, and a plurality of second sliding surfaces between the second inner ring and the second outer ring and the second rolling element slide against each other. According to this invention, depending on the magnitude of the first friction torque and the second friction torque, a state is switched between where the first rolling bearing operates, the multiple first sliding surfaces slide against each other, and the second rolling bearing is stationary, and a state where the second rolling bearing operates, the multiple second sliding surfaces slide against each other, and the first rolling bearing is stationary. In this way, the multiple sliding surfaces sliding against each other can be alternately switched between the multiple first sliding surfaces and the multiple second sliding surfaces.

[0013] The bearing system of the present invention further comprises a shaft portion, a first bearing device and a second bearing device which are any of the bearing devices described above, and a second connecting member fixed to the second outer ring of the first bearing device and the second outer ring of the second bearing device, respectively, wherein the first bearing device and the second bearing device are arranged side by side along the axial direction of the first rolling bearing in the first bearing device, and the shaft portion is fixed to the first inner ring of the first bearing device and the first inner ring of the second bearing device, respectively.

[0014] According to this invention, by supporting two axial positions of the shaft portion by the first inner rings of the first bearing device and the second bearing device, it is possible to prevent the shaft portion from tilting relative to the axes of the first bearing device and the second bearing device. Furthermore, by supporting the second connecting member, it is possible to easily support the entire bearing system. Effect of the Invention

[0015] According to the bearing device and bearing system of the present invention, it is possible to suppress an increase in friction torque generated within the bearing device and bearing system, thereby achieving a long service life. [Brief description of the drawings]

[0016] [Figure 1] 1 is a cross-sectional view of a main portion of an artificial satellite in which a bearing device according to an embodiment of the present invention is used. [Diagram 2] FIG. 1 is a cross-sectional view of a conventional bearing device. [Diagram 3] FIG. 11 is a cross-sectional view of a bearing device according to a modified example of an embodiment of the present invention. [Figure 4]FIG. 13 is a diagram showing the change in output torque of a VCM with respect to the number of oscillation cycles in a conventional bearing system. [Diagram 5] FIG. 11 is a diagram showing a change in output torque of a VCM relative to the number of oscillation cycles in the bearing system of the embodiment. [Figure 6] FIG. 11 is a diagram showing changes in the mirror angle etc. with respect to the number of oscillation cycles in the bearing system of the embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] Hereinafter, one embodiment of a bearing system according to the present invention will be described with reference to Figs. 1 to 6, taking as an example a case in which the bearing system is used in an artificial satellite. As shown in FIG. 1, the artificial satellite 1 includes a structure 10 and a bearing system 15 of this embodiment. The structure 10 constitutes the basic structure of the artificial satellite 1 .

[0018] The bearing system 15 includes a shaft portion 16, a housing (second connecting member) 21, and a first bearing device (bearing device) 31 and a second bearing device (bearing device) 56 of the present embodiment. Shaft portion 16 is rod-shaped and extends in the direction of a predetermined axis O. Shaft portion 16 has a small diameter portion 17 and a large diameter portion 18. The outer diameter of large diameter portion 18 is larger than the outer diameter of small diameter portion 17. The axis O is a common axis with the axis of a first rolling bearing 33 of the first bearing device 31, which will be described later, and the axis of a first rolling bearing 58 of the second bearing device 56, which will be described later. Hereinafter, the direction from the large diameter portion 18 toward the small diameter portion 17 will be referred to as the tip side. The side opposite the tip side will be referred to as the base side. When viewing the bearing system 15 from the direction of the axis O, the direction perpendicular to the axis O will be referred to as the radial direction, and the direction going around the axis O will be referred to as the circumferential direction.

[0019] At the tip of the large diameter portion 18, locking portions 18a, 18b are formed which protrude radially outward from the outer circumferential surface of the large diameter portion 18. Locking portion 18a is disposed on the tip side of locking portion 18b. Locking portion 18a is disposed at the tip of the large diameter portion 18. A locking portion 18c is formed at the base end of the large diameter portion 18, protruding radially outward from the outer circumferential surface of the large diameter portion 18. The locking portion 18c is disposed on the tip side of the large diameter portion 18 relative to the base end. The locking portions 18a, 18b, and 18c are each formed on the large diameter portion 18 over the entire circumference in the circumferential direction. The small diameter portion 17 and the large diameter portion 18 are continuous with each other in the axis O direction. A mirror 19 and a magnet 20 are fixed between the locking portion 18b and the locking portion 18c of the large diameter portion 18. For example, the magnet 20 is disposed on the opposite side of the large diameter portion 18 from the mirror 19.

[0020] The housing 21 has a distal housing 22, a proximal housing 23, and a connecting housing 24. The distal housing 22 is disposed on the distal side of the proximal housing 23. The tip housing 22 has a cylindrical portion 22a and an annular portion 22b. The cylindrical portion 22a is cylindrical. The cylindrical portion 22a is arranged coaxially with the axis O. The cylindrical portion 22a covers the small diameter portion 17 of the shaft portion 16 from the radially outer side. The annular portion 22b extends radially inward from the tip end of the cylindrical portion 22a. The annular portion 22b is formed around the entire circumference of the cylindrical portion 22a in the circumferential direction. The base end housing 23 has a cylindrical portion 23a and an annular portion 23b. The cylindrical portion 23a is cylindrical. The cylindrical portion 23a is arranged coaxially with the axis O. The cylindrical portion 23a is arranged closer to the base end than the shaft portion 16. The annular portion 23b extends radially inward from the base end of the cylindrical portion 23a. The annular portion 23b is formed around the entire circumference of the cylindrical portion 23a in the circumferential direction.

[0021] The connecting housing 24 has a first connecting piece 24a, a second connecting piece 24b, and a third connecting piece 24c. The first connecting piece 24a extends radially outward from a portion of the outer circumferential surface of the cylindrical portion 22a of the tip housing 22. The second connecting piece 24b extends radially outward from a portion of the outer circumferential surface of the cylindrical portion 23a of the base housing 23. The third connecting piece 24c connects the tip end from which the first connecting piece 24a extends and the tip end from which the second connecting piece 24b extends. The third connecting piece 24c extends in the axis O direction.

[0022] An electromagnetic coil 25 is fixed to the outer surface of the third connecting piece 24c of the connecting housing 24 on the shaft portion 16 side. The electromagnetic coil 25 and the magnet 20 constitute a VCM (Voice Coil Motor) 26. The electromagnetic coil 25 is disposed so as to face the magnet 20, i.e., so that a gap is formed between the electromagnetic coil 25 and the magnet 20. The outer surface of the third connecting piece 24 c of the housing 21 configured as above, opposite to the shaft portion 16 , is fixed to the body structure 10 and supported by the body structure 10 .

[0023] The first bearing device 31 and the second bearing device 56 are arranged side by side along the direction of the axis O. The first bearing device 31 and the second bearing device 56 are arranged so as to sandwich the mirror 19, the magnet 20, and the electromagnetic coil 25 in the direction of the axis O. The first bearing device 31 includes a redundant housing (first connecting member) 32, a pair of first rolling bearings 33, and a pair of second rolling bearings 34. The redundant housing 32 has a first cylindrical portion (first cylindrical member) 37, a first annular portion (annular member) 38, a second cylindrical portion (second cylindrical member) 39, and a second annular portion 40. The first cylindrical portion 37 and the second cylindrical portion 39 are each cylindrical. The first cylindrical portion 37 and the second cylindrical portion 39 are each arranged coaxially with the axis O. The first cylindrical portion 37 covers the radial outside of the small diameter portion 17 of the shaft portion 16. The first annular portion 38 extends radially outward from a base end portion 37a of the first cylindrical portion 37. The first annular portion 38 is formed over the entire circumferential circumference of the first cylindrical portion 37. A base end face 38a of the first annular portion 38 is disposed at a position equivalent to a base end face 18a1 of the locking portion 18a of the shaft portion 16 in the direction of the axis O.

[0024] The second cylindrical portion 39 extends from the radially outer end of the first annular portion 38 toward the base end. The second cylindrical portion 39 covers the tip end of the large diameter portion 18 of the shaft portion 16 from the radially outer side. The first annular portion 38 connects the base end (end in the direction of axis O) of the first cylindrical portion 37 and the tip end (in the direction of axis O) of the second cylindrical portion 39. The second annular portion 40 extends radially inward from the base end of the second cylindrical portion 39. The second annular portion 40 is formed around the entire circumferential circumference of the second cylindrical portion 39. A tip end face of the second annular portion 40 is disposed at a position equivalent to a tip end face of the locking portion 18b of the shaft portion 16 in the axis O direction. As described above, the redundant housing 32 has a rotationally symmetric shape about the axis O.

[0025] In the first rolling bearing 33, a first inner ring 43 and a first outer ring 44 are connected via a first ball (first rolling element) 45. The first inner ring 43 and the first outer ring 44 are each annular. In the first rolling bearing 33, the first ball 45 rolls between the first inner ring 43 and the first outer ring 44. Here, the surfaces that slide against each other between the first inner ring 43 and the first outer ring 44 and the first ball 45 are referred to as first sliding surfaces 43a, 44a, and 45a. Specifically, the first sliding surface 43a is the outer surface of the first inner ring 43 that is rubbed by the first ball 45. The first sliding surface 44a is the outer surface of the first outer ring 44 that is rubbed by the first ball 45. The first sliding surface 45a is the outer surface of the first ball 45 that is rubbed by the first inner ring 43 and the first outer ring 44. The friction torque generated between the first inner ring 43 and the first outer ring 44 via the first balls 45 is defined as a first friction torque.

[0026] The pair of first rolling bearings 33 are arranged side by side along the axis O (positionally shifted in the axis O direction). The first inner rings 43 of the pair of first rolling bearings 33 are fixed to the outer peripheral surface of the tip end of the large diameter portion 18 of the shaft portion 16. The first inner rings 43 of the pair of first rolling bearings 33 are sandwiched in the axis O direction by the locking portions 18a, 18b of the shaft portion 16. The first outer rings 44 of the pair of first rolling bearings 33 are fixed to the inner circumferential surface of the second cylindrical portion 39 of the redundant housing 32. Shrink fitting, bolts, etc. are used as fixing means for fixing the first outer rings 44 to the second cylindrical portion 39. The first outer rings 44 of the pair of first rolling bearings 33 are sandwiched between the annular portions 38, 40 of the redundant housing 32 in the axis O direction.

[0027] In the second rolling bearing 34, a second inner ring 48 and a second outer ring 49 are connected via a second ball (second rolling element) 50. In the second rolling bearing 34, the second ball 50 rolls between the second inner ring 48 and the second outer ring 49. Here, the surfaces that slide against each other between the second inner ring 48 and the second outer ring 49 and the second ball 50 are referred to as second sliding surfaces 48a, 49a, 50a. Specifically, the second sliding surface 48a is the outer surface of the second inner ring 48 that is rubbed by the second ball 50. The second sliding surface 49a is the outer surface of the second outer ring 49 that is rubbed by the second ball 50. The second sliding surface 50a is the outer surface of the second ball 50 that is rubbed by the second inner ring 48 and the second outer ring 49. The friction torque generated between the second inner ring 48 and the second outer ring 49 via the second balls 50 is defined as a second friction torque.

[0028] The pair of second rolling bearings 34 are arranged side by side along the direction of the axis O. The second rolling bearings 34 have the same configuration as the first rolling bearing 33. That is, the first rolling bearing 33 and the second rolling bearing 34 have the same inner diameter and the same outer diameter. The pair of first rolling bearings 33 and the pair of second rolling bearings 34 are coaxial with each other and arranged side by side in the direction of the axis O. The first friction torque and the second friction torque are equal to each other. However, due to individual differences in the rolling bearings 33 and 34, the first friction torque and the second friction torque may differ from each other.

[0029] The second inner ring 48 of the pair of second rolling bearings 34 is fixed to the outer circumferential surface of the first cylindrical portion 37 of the redundant housing 32. Shrink fitting, bolts, etc. are used as fixing means for fixing the second inner ring 48 to the first cylindrical portion 37. The first annular portion 38 of the redundant housing 32 comes into contact with the second inner ring 48 of the second rolling bearing 34 on the base end side from the base end side of the second inner ring 48. The second outer ring 49 of the pair of second rolling bearings 34 is fixed to the inner circumferential surface of the cylindrical portion 22a of the tip housing 22 of the housing 21. The annular portion 22b of the tip housing 22 of the redundant housing 32 comes into contact with the second outer ring 49 of the second rolling bearing 34 on the tip side from the tip side of the second outer ring 49.

[0030] In the first bearing device 31 configured as above, a so-called fixed position preload is used as a method of preloading the shaft portion 16. That is, for example, the pair of first rolling bearings 33 are fastened in the direction of the axis O by the locking portions 18a, 18b, and a preload is applied to the pair of first rolling bearings 33. The first bearing device 31 is a redundant bearing device that includes two rolling bearings 33, 34 connected in series between the shaft portion 16 and the housing 21.

[0031] The second bearing device 56 includes a redundant housing (first connecting member) 57, a first rolling bearing 58, and a second rolling bearing 59. The redundant housing 57 has a cylindrical portion 62, a first cylindrical portion 63, an annular portion 64, and a second cylindrical portion 65. The cylindrical portion 62 has a cylindrical shape. The cylindrical portion 62 is disposed coaxially with the axis O. The cylindrical portion 62 is disposed closer to the base end than the shaft portion 16. The first cylindrical portion 63 and the second cylindrical portion 65 are each cylindrical. The first cylindrical portion 63 extends from the outer circumferential edge of the columnar portion 62 toward the tip side. The first cylindrical portion 63 is formed on the columnar portion 62 over the entire circumference in the circumferential direction. The annular portion 64 extends radially outward from the tip end of the first cylindrical portion 63. The annular portion 64 is formed on the first cylindrical portion 63 over the entire circumference in the circumferential direction. The second cylindrical portion 65 extends from the outer circumferential edge of the annular portion 64 toward the tip side. The second cylindrical portion 65 is formed over the entire circumferential circumference of the annular portion 64. The second cylindrical portion 65 covers the base end portion of the large diameter portion 18 of the shaft portion 16 from the radial outside. As described above, the redundant housing 57 has a shape that is rotationally symmetric about the axis O.

[0032] In the first rolling bearing 58, a first inner ring 68 and a first outer ring 69 are connected via first balls (first rolling elements) 70. The first inner ring 68 of the first rolling bearing 58 is fixed to the outer peripheral surface of the base end of the large diameter portion 18 of the shaft portion 16. The first inner ring 68 of the first rolling bearing 58 comes into contact with the locking portion 18c of the shaft portion 16 from the tip side of the first inner ring 68. The first outer ring 69 of the first rolling bearing 58 is fixed to the inner circumferential surface of the second cylindrical portion 65 of the redundant housing 57. The annular portion 64 of the redundant housing 57 comes into contact with the first outer ring 69 of the first rolling bearing 58 from the base end side relative to the first outer ring 69. In the second rolling bearing 59, a second inner ring 73 and a second outer ring 74 are connected via second balls (second rolling elements) 75. The second rolling bearing 59 has the same configuration as the first rolling bearing 58. That is, the first rolling bearing 58 and the second rolling bearing 59 have the same inner diameter and the same outer diameter.

[0033] The second inner ring 73 of the second rolling bearing 59 is fixed to the outer circumferential surface of the first cylindrical portion 63 of the redundant housing 57. The second rolling bearing 59 and the annular portion 64 of the redundant housing 57 are spaced apart in the axis O direction. The second outer ring 74 of the second rolling bearing 59 is fixed to the inner circumferential surface of the cylindrical portion 23a of the base end housing 23 of the housing 21. The annular portion 23b of the base end housing 23 of the redundant housing 57 contacts the second outer ring 74 of the second rolling bearing 59 from the base end side relative to the second outer ring 74, via the spring 23c. The spring 23c urges the second outer ring 74 of the second rolling bearing 59 toward the tip end side. In the second bearing device 56 configured as above, a so-called constant pressure preload is used as a method for preloading the shaft portion 16. That is, the spring 23c presses the second rolling bearing 59 toward the tip side, and the first rolling bearing 58 is pressed toward the tip side via the redundant housing 57.

[0034] Next, the operation of the artificial satellite 1 configured as above will be described, with emphasis on the operation of the bearing system 15. For example, it is assumed that the artificial satellite 1 is placed in orbit around the earth, that a number of observation points are set on the ground, and that the mirror 19 is controlled to point toward the multiple observation points in turn. For example, when the orientation of mirror 19 switches between a first observation point and a second observation point among the multiple observation points, shaft portion 16 rotates around axis O so as to oscillate by a small angle. In the following description, it is assumed that in the second bearing device 56, the rolling bearings 58, 59 in operation are not switched.

[0035] When the bearing system 15 starts operating, in the first bearing device 31, the first friction torque generated by the pair of first rolling bearings 33 is smaller than the second friction torque generated by the pair of second rolling bearings 34. The pair of first rolling bearings 33 are operating, and the pair of second rolling bearings 34 are stopped. This state is called a first operating state of the first bearing device 31. In the first operating state, the first sliding surfaces 43a, 44a, and 45a of the pair of first rolling bearings 33 slide against each other. To explain in more detail, the sliding surface 43a and the sliding surface 45a slide against each other, and the sliding surface 44a and the sliding surface 45a slide against each other. When an electric current is applied to the electromagnetic coil 25 of the VCM 26, the mirror 19 fixed to the shaft portion 16 swings around the axis O due to the magnetic force acting between the electromagnetic coil 25 and the magnet 20.

[0036] When the bearing system 15 operates for a certain period of time, the first friction torque becomes larger than the second friction torque due to wear of the first sliding surfaces 43a, 44a, 45a, etc., and the pair of second rolling bearings 34 operates more easily than the pair of first rolling bearings 33. Then, the pair of first rolling bearings 33 stops, and the pair of second rolling bearings 34 operates, switching to a second operating state of the first bearing device 31. In the second operating state, the second sliding surfaces 48a, 49a, 50a of the pair of second rolling bearings 34 slide against each other. To explain in more detail, the sliding surface 48a and the sliding surface 50a slide against each other, and the sliding surface 49a and the sliding surface 50a slide against each other. At this time, the phase of the first inner ring 43 and the first outer ring 44 in the first rolling bearing 33 is shifted, and the first friction torque is likely to become small.

[0037] When the bearing system 15 operates for a certain period of time, the second friction torque becomes larger than the first friction torque due to wear of the second sliding surfaces 48a, 49a, 50a, etc., and the pair of first rolling bearings 33 operates more easily than the pair of second rolling bearings 34. Then, the first bearing device 31 transitions to the first operating state. At this time, the phase of the second inner ring 48 and the second outer ring 49 of the second rolling bearing 34 shifts, and the second friction torque tends to become smaller. As described above, the first bearing device 31 is configured to be alternately switched between the first operating state and the second operating state.

[0038] In practice, the rolling bearings 58, 59 operating in the second bearing device 56 alternate in the same way that the first bearing device 31 alternates between a first and a second operating state.

[0039] In contrast, in a conventional bearing device 100 shown in FIG. 2, one rolling bearing 103 is disposed between a shaft portion 101 and a housing 102.

[0040] As described above, in the first bearing device 31 of this embodiment, the second outer ring 49 of the second rolling bearing 34 is supported by the housing 21. For example, when the first friction torque by the first rolling bearing 33 is smaller than the second friction torque by the second rolling bearing 34, the second rolling bearing 34 stops, and the shaft portion 16 and the first inner ring 43 rotate together with the first outer ring 44, the redundant housing 32, and the second rolling bearing 34 around the axis O. When the first friction torque becomes larger than the second friction torque, the first rolling bearing 33 stops, and the shaft portion 16, the first rolling bearing 33, the redundant housing 32, and the second inner ring 48 rotate together with the second outer ring 49 around the axis O. In this way, even if the first rolling bearing 33 stops, the second rolling bearing 34 can rotate the shaft portion 16 about the axis O. Therefore, compared to when the first bearing device is equipped with only one rolling bearing, it is possible to prevent the friction torque generated in the first bearing device 31 from increasing, and the first bearing device 31 can have a longer life.

[0041] The first rolling bearing 33 and the second rolling bearing 34 are coaxial with each other and arranged side by side along the direction of the axis O. This makes it possible to prevent the outer diameter of the first bearing device 31 in the direction perpendicular to the axis O from becoming large. The first rolling bearing 33 and the second rolling bearing 34 have the same inner diameter and the same outer diameter. Therefore, the first friction torque of the first rolling bearing 33 and the second friction torque of the second rolling bearing 34 can be easily made equal to each other. Therefore, the magnitude relationship between the two friction torques can be easily switched, and it is possible to easily switch between a first operating state in which the first rolling bearing 33 is operating and the second rolling bearing 34 is stopped, and a second operating state in which the first rolling bearing 33 is stopped and the second rolling bearing 34 is operating.

[0042] The redundant housing 32 has a shape that is rotationally symmetric about the axis O. Therefore, it is possible to stabilize the movement of the redundant housing 32 when the redundant housing 32 rotates about the axis O. As a result, it is possible to stabilize the movement of each of the first rolling bearing 33 and the second rolling bearing 34 fixed to the redundant housing 32 about the axis O. The redundant housing 32 has a first cylindrical portion 37, a first annular portion 38, a second cylindrical portion 39, and a second annular portion 40. Therefore, the redundant housing 32 can be easily configured by the four members, namely, the first cylindrical portion 37, the first annular portion 38, the second cylindrical portion 39, and the second annular portion 40.

[0043] The first bearing device 31 is configured to switch from a first operating state in which the first friction torque is smaller than the second friction torque, the second rolling bearing 34 is stopped, and the first sliding surfaces 43a, 44a, 45a of the first rolling bearing 33 slide against each other, to a second operating state in which the first friction torque is larger than the second friction torque, the first rolling bearing 33 is stopped, and the second sliding surfaces 48a, 49a, 50a of the second rolling bearing 34 slide against each other. Therefore, depending on the magnitude of the first friction torque and the second friction torque, the first bearing device 31 switches between a first operating state in which the first rolling bearing 33 operates, the first sliding surfaces 43a, 44a, 45a slide against each other, and the second rolling bearing 34 is stopped, and a second operating state in which the second rolling bearing 34 operates, the second sliding surfaces 48a, 49a, 50a slide against each other, and the first rolling bearing 33 is stopped. In this way, the sliding surfaces that slide against each other can be alternately switched between the first sliding surfaces 43a, 44a, 45a and the second sliding surfaces 48a, 49a, 50a.

[0044] Since the first bearing device 31 includes the pair of first rolling bearings 33, it is possible to prevent the shaft portion 16 from tilting relative to the axis of the pair of first rolling bearings 33. The same applies to the pair of second rolling bearings . Furthermore, in the bearing system 15 of this embodiment, two points on the shaft portion 16 in the direction of the axis O are supported by the first inner ring 43 of the first bearing device 31 and the first inner ring 68 of the second bearing device 56, respectively, thereby making it possible to prevent the shaft portion 16 from tilting relative to the axes of the first bearing device 31 and the second bearing device 56. Furthermore, by supporting the housing 21, the entire bearing system 15 can be easily supported. By configuring the first bearing device 31 to have a fixed position preload, the first bearing device 31 can be made highly rigid.

[0045] In this embodiment, the first bearing device 31A may include one each of the first rolling bearing 33 and the second rolling bearing 34, as in a bearing system 15A shown in FIG. The first bearing device may comprise three or more rolling bearings connected in series with each other, as may the second bearing device.

[0046] Although one embodiment of the present invention has been described in detail above with reference to the drawings, the specific configuration is not limited to this embodiment, and changes, combinations, deletions, etc. of the configuration are also included within the scope that does not deviate from the gist of the present invention. For example, in the above-described embodiment, the first rolling bearing and the second rolling bearing may have different inner diameters and / or outer diameters. The second rolling bearing may be disposed radially outward relative to the first rolling bearing. The redundant housings 32 and 57 do not have to have a shape that is rotationally symmetric about the axis O. The redundant housing 32 does not have to have the second annular portion 40. In this case, the redundant housing 32 can be easily configured using three members, namely, the first cylindrical portion 37, the first annular portion 38, and the second cylindrical portion 39. Although the first rolling element is described as a first ball, the first rolling element may be a first roller, etc. The same applies to the second rolling element.

[0047] [Experimental result 1] Vibration tests were conducted using the bearing system of the embodiment and a conventional bearing system. As vibration waveforms, sine waves and random waveforms used in qualification tests for artificial satellites were used. In the conventional bearing system, the bearing device does not include multiple rolling bearings connected in series. The axial movement of the redundant housing relative to the housing was measured by a rotary sensor. The shaft was rotated using a VCM, so that the output torque of the VCM corresponds to the friction torque of the bearing system.

[0048] In both Fig. 4 and Fig. 5, the horizontal axis represents the number of oscillation cycles (times), and the vertical axis represents the output torque of the VCM (Nm (Newton meters)). In the conventional bearing system shown in FIG. 4, although only a portion is shown, the number of oscillation cycles is 10 7 As the number of rotations increased, the output torque increased about five times. On the other hand, in the bearing system of the embodiment shown in FIG. 5, although only a part of it is shown, the number of oscillation cycles is 10 7 Even at this speed, there was almost no increase in output torque.

[0049] [Experimental result 2] Figure 6 shows the change in the mirror angle, VCM actual load factor, and rotary sensor value versus the number of oscillation cycles when using the bearing system of the embodiment. Here, the VCM actual load factor means the ratio of the current flowing through the VCM to the VCM's upper limit allowable current value, expressed as a percentage (maximum 100%). Curve L1 represents the mirror angle (deg). Curve L2 represents the VCM actual load factor (%), and curve L3 represents the rotary sensor value (deg). Feedback control was performed so that the amplitude of the mirror angle was 0.3 deg. As the number of oscillation cycles approached N0, the friction torque of the rolling bearing increased, and the VCM actual load rate increased, causing an overshoot in the oscillation angle, which in turn caused the feedback control to become ineffective. When the number of oscillation cycles is N0, for example, the first operating state is switched to the second operating state, and the rotary sensor value increases. When the first operating state is switched to the second operating state, the feedback control becomes more effective, and it can be seen that the VCM actual load factor decreases. When the number of oscillation cycles is further increased, the second operating state is switched to the first operating state. [Explanation of symbols]

[0050] 15,15A Bearing System 16 Shaft 21 Housing (second connecting member) 31 First bearing device (bearing device) 32,57 Redundant housing (first connecting member) 33,58 First rolling bearing 34,59 Second rolling bearing 37 First cylindrical portion (first cylindrical member) 38 First annular portion (annular member) 39 Second cylindrical portion (second cylindrical member) 43,68 First inner ring 43a,44a,45a 1st sliding surface 44,69 First outer wheel 45,70 First ball (first rolling element) 48,73 Second inner ring 48a,49a,50a 2nd sliding surface 49,74 Second outer wheel 50,75 Second ball (second rolling element) 56 Second bearing device (bearing device) O axis

Claims

1. a first rolling bearing in which a first inner ring and a first outer ring are connected via a first rolling element; a second rolling bearing in which a second inner ring and a second outer ring are connected via a second rolling element; a first connecting member fixed to the first outer ring and the second inner ring, A friction torque generated between the first inner ring and the first outer ring via the first rolling element is defined as a first friction torque, When the friction torque generated between the second inner ring and the second outer ring via the second rolling element is defined as a second friction torque, From a state in which the first friction torque is smaller than the second friction torque, the second rolling bearing is stopped, and a plurality of first sliding surfaces between the first inner ring and the first outer ring and the first rolling element slide against each other, The bearing device is configured so that when the first friction torque becomes greater than the second friction torque, the first rolling bearing stops and a state is switched to in which a plurality of second sliding surfaces between the second inner ring and the second outer ring and the second rolling body slide against each other.

2. The bearing device according to claim 1 , wherein the first rolling bearing and the second rolling bearing are coaxial with each other and arranged side by side along an axial direction of the first rolling bearing.

3. 3. The bearing device according to claim 2, wherein the first rolling bearing and the second rolling bearing have the same inner diameter and the same outer diameter.

4. The bearing device according to claim 1 , wherein the first connecting member has a shape that is rotationally symmetric about an axis of the first rolling bearing.

5. The first connecting member is a first cylindrical member fixed to the second inner ring; a second cylindrical member fixed to the first outer ring; 5. A bearing device according to claim 1, further comprising an annular member connecting an axial end of the first rolling bearing in the first cylindrical member and an axial end of the second cylindrical member.

6. A shaft portion, A first bearing device and a second bearing device, which are the bearing devices according to any one of claims 1 to 5; a second connecting member fixed to the second outer ring of the first bearing device and the second outer ring of the second bearing device, the first bearing device and the second bearing device are arranged side by side along an axial direction of the first rolling bearing of the first bearing device, A bearing system, wherein the shaft portion is fixed to the first inner ring of the first bearing device and the first inner ring of the second bearing device, respectively.

Images