WO2023032916A1 - Joint mechanism, parallel link mechanism, and link actuation device - Google Patents

Abstract

Provided is a parallel link mechanism comprising a bearing (23) in each of revolute pair parts including revolute pair parts each between a link hub (12) on a base end side and an end portion link member (15) on the base end side, revolute pair parts each between each of end portion link members on the base end side and a distal end side and a center link member (17), and revolute pair parts each between a link hub on the distal end side and the end portion link member on the distal end side. The bearing (23) is a grease-sealed bearing provided with a grease composition sealed into a bearing space between inner and outer rings. The grease composition contains a base oil and a thickener and has a worked penetration of 310 or more. The thickener is a calcium sulfonate complex soap or a lithium soap.

Description

Joint mechanism, parallel link mechanism and link actuator Related application

This application claims the priority of Japanese Patent Application No. 2021-144317 filed on September 3, 2021, and is incorporated herein by reference in its entirety.

The present invention relates to a joint mechanism, a parallel link mechanism, and a link actuator used in equipment that requires high speed, high precision, and a wide operating range, such as medical equipment or industrial equipment.

In Patent Document 1, a working device which has a base plate and a traveling plate, which are connected by a plurality of links, and performs a predetermined work by means of a parallel link mechanism that moves the traveling plate by cooperating these links. is proposed.
Patent Literature 2 proposes a link actuating device that is compact, high-speed, highly accurate, and capable of operating in a wide operating range.

JP-A-2000-94245 U.S. Pat. No. 5,893,296

In the parallel link mechanism of Patent Document 1, each link has a small operating angle. Therefore, in order to increase the operating range of the traveling plate, it is necessary to lengthen the link length. As a result, there is a problem that the size of the entire mechanism is increased, resulting in an increase in the size of the device. Also, increasing the length of the link leads to a reduction in the rigidity of the entire mechanism. Therefore, there is also a problem that the weight of the tool mounted on the traveling plate, that is, the weight capacity of the traveling plate is also limited to a small one.

In the configuration of the parallel link mechanism and the link actuation device shown in Patent Document 2, each of the rotating pair portions oscillates, and for the bearings installed in the rotating pair portions, the stop-start-run-stop operation per unit time is required. The number of switching times increases. Therefore, the acceleration and deceleration applied to the bearing each time increase, resulting in increased slippage of the bearing. The slippage that occurs in the bearing makes it easier for the oil film to run out between the rolling elements and the bearing rings. As a result, local wear called fretting wear tends to occur on the surfaces of the rolling elements or on the raceway surfaces of the inner and outer rings, possibly shortening the life of the bearing. In addition, if the bearing is slightly oscillated under high preload, the grease will cause a so-called "jamming," in which the rotational torque of the bearing will increase in some areas during rotation, making it impossible to rotate smoothly. I was afraid it would disappear.

An object of the present invention is to provide a joint mechanism, a parallel link mechanism, and a link operating device that are capable of high-speed operation over a wide operating range, and that achieve long life and smooth movement.

A joint mechanism of the present invention is a joint mechanism in which adjacent members are rotatably connected to each other via a rotating pair portion, and a grease-filled bearing in which a grease composition is sealed is provided in the rotating pair portion,
The grease composition contains a base oil and a thickener and has a worked penetration of 310 or more,
The thickener is calcium sulfonate complex soap or lithium soap.
The "worked penetration" is a 60-fold worked penetration in accordance with JIS K 2220.

By applying the above-mentioned grease composition, the inflow of grease to, for example, the contact portion between the rolling element and the bearing ring in the bearing is improved, and the fretting wear resistance is excellent. In addition, when the grease-filled bearing is used in the rotating pair portion, even if the bearing is slightly oscillated in a high preload state, catching during subsequent rotation is reduced and high-speed operation becomes possible. Therefore, it is possible to realize a joint mechanism that is capable of high-speed operation in a wide operating range, has a long service life, and achieves smooth movement.

In the parallel link mechanism of the present invention, a link hub on the distal end side is connected to a link hub on the proximal end side via three or more sets of link mechanisms so that the attitude can be changed, and each of the link mechanisms is connected to the link hub on the proximal end side. a proximal end link member having one end rotatably connected to a link hub; a distal end link member having one end rotatably connected to the distal link hub; a center link member rotatably connected at both ends to the other end of the end link member on the tip side;
A rotational pair portion between the proximal link hub and the proximal end link member, a rotational pair portion between the proximal end link member and the central link member, and the distal end link. A bearing is provided at each rotational pair portion including a rotational pair portion between the member and the central link member and a rotational pair portion between the tip side link hub and the tip side end link member, and a plurality of the bearings at least one bearing in is a grease-filled bearing comprising inner and outer rings that are bearing rings, a plurality of rolling elements interposed between the inner and outer rings, and a grease composition sealed in the bearing space between the inner and outer rings A parallel link mechanism,
The grease composition contains a base oil and a thickener and has a worked penetration of 310 or more,
The thickener is calcium sulfonate complex soap or lithium soap.
The "worked penetration" is a 60-fold worked penetration in accordance with JIS K 2220.

According to this configuration, the link hub on the base end side, the link hub on the tip side, and three or more sets of link mechanisms are arranged so that the link hub on the tip side can rotate about two orthogonal axes with respect to the link hub on the base end side. A degree of freedom mechanism is configured. In other words, the link hub on the distal end side has two degrees of freedom in rotation with respect to the link hub on the proximal end side, and the posture can be freely changed. This two-degrees-of-freedom mechanism is compact, but allows a wide movable range of the link hub on the distal end side with respect to the link hub on the proximal end side.

This parallel link mechanism performs an oscillating motion in which each rotational pair is near ±θmax/2 with respect to the maximum bending angle θmax, which is the operating range. The revolving motion of the rolling elements is 1/2 of the rocking motion of the rotating pair. Moreover, the rigidity of the parallel link mechanism largely contributes to the moment rigidity of the bearing, and the bearing is often used under high preload. A grease-encapsulated bearing in which the following grease composition is enclosed is applied to the rotating pair portion of the present parallel link mechanism. The grease composition contains a base oil and a thickener, has a worked penetration of 310 or more, and the thickener is a calcium sulfonate complex soap or a lithium soap. As a result, the grease can easily flow into the contact portion between the rolling element and the bearing ring, resulting in excellent fretting wear resistance. In addition, when the grease-filled bearing is used in the rotating pair portion, even if the bearing is slightly oscillated in a high preload state, catching during subsequent rotation is reduced and high-speed operation becomes possible. Therefore, it is possible to realize a parallel link mechanism that is capable of high-speed operation over a wide operating range and that achieves a long life and smooth movement.

The grease-filled bearing may be used under a high load condition in which the maximum contact surface pressure on the bearing ring is 2000 MPa or more and under a condition of less than the critical swing angle.
The "maximum contact surface pressure" is the maximum value of the surface pressure on the contact surface between the bearing ring and the rolling element.
The "critical swing angle" is the minimum practical swing angle of a bearing, and is determined mainly by the number of rolling elements included in a single row in the internal design of the bearing. be.
This grease-filled bearing has sufficient fretting wear resistance and sealing performance even under the high load condition and under the condition of less than the critical swing angle.

In the grease composition, the thickener may be a calcium sulfonate complex soap, and the worked penetration may be 310-340. In this case, the fluidity of the grease is restricted to a predetermined range, resulting in better sealing performance.

The base oil of the grease composition may be mineral oil or synthetic hydrocarbon oil. The combination of base oil and thickener is involved in the interaction between the thickeners in the base oil and affects the thickening effect. Therefore, it is preferable to select an appropriate combination. When the base oil is mineral oil, the cost can be reduced compared to using a synthetic hydrocarbon oil. When the base oil is a synthetic hydrocarbon oil, lubricating performance at high temperatures is obtained better than using mineral oil.

The grease-filled bearing may be an angular contact ball bearing. In this case, an axial load can be applied in advance to the angular contact ball bearing to increase the rigidity of the bearing. Therefore, it is possible to improve the accuracy of the parallel link mechanism.

The angular contact ball bearing may be a combination angular contact ball bearing used back to back. The stiffness of the parallel link mechanism greatly contributes to the moment stiffness of the bearing. Therefore, by using a back-to-back paired angular contact ball bearing, it is possible to increase the moment rigidity of the bearing with an inexpensive bearing structure. As a result, the rigidity of the parallel link mechanism can be increased and the cost can be reduced.

The paired angular contact ball bearing may be provided with a seal member on the axial outer surface opposite to the mating surface. In this case, it is possible to prevent foreign matter from entering the bearing and grease leakage from the bearing with a minimum number of parts. Also, the orientation of the bearings to be installed when assembling the parallel link mechanism can be easily determined by the presence or absence of the seal member. Therefore, assemblability is improved, leading to cost reduction.

In the grease composition of the present invention, a link hub on the distal end side is connected to a link hub on the proximal end side via three or more sets of link mechanisms so that the attitude can be changed, and each of the link mechanisms is connected to the link hub on the proximal end side. a proximal end link member having one end rotatably connected to a link hub; a distal end link member having one end rotatably connected to the distal link hub; A grease composition for use in a parallel link mechanism having a central link member rotatably connected at both ends to the other end of the end link member on the tip side,
The grease composition contains a base oil and a thickener and has a worked penetration of 310 or more,
The thickener is calcium sulfonate complex soap or lithium soap.
The "worked penetration" is a 60-fold worked penetration in accordance with JIS K 2220.

By using the grease composition in each contact portion of the parallel link mechanism, the inflow of grease to the contact portion is improved and the fretting wear resistance is excellent.

In the bearing of the present invention, the link hub on the front end side is connected to the link hub on the base end side through three or more sets of link mechanisms so that the posture can be changed, and each of the link mechanisms is connected to the link hub on the base end side. a proximal end link member having one end rotatably connected to the distal end link hub; a distal end link member having one end rotatably connected to the distal link hub; A bearing used in a parallel link mechanism having a center link member rotatably connected at both ends to the other end of the side end link member,
The bearing includes a rotational pair portion between the proximal side link hub and the proximal side end link member, a rotational pair portion between the proximal side end link member and the central link member, and the distal end side. provided in each rotational pair portion including a rotational pair portion between the end link member and the central link member, and a rotational pair portion between the tip side link hub and the tip side end link member, and a plurality of At least one of the bearings includes inner and outer rings as bearing rings, a plurality of rolling elements interposed between the inner and outer rings, and a grease composition sealed in a bearing space between the inner and outer rings. a bearing,
The grease composition contains a base oil and a thickener and has a worked penetration of 310 or more,
The thickener is calcium sulfonate complex soap or lithium soap.
The "worked penetration" is a 60-fold worked penetration in accordance with JIS K 2220.

In this case, the grease can easily flow into the contact area between the rolling element and the bearing ring, resulting in excellent fretting wear resistance. In addition, when the grease-filled bearing is used in the rotating pair portion, even if the bearing is slightly oscillated in a high preload state, catching during subsequent rotation is reduced and high-speed operation becomes possible.

The link actuating device of the present invention arbitrarily controls the posture of the link hub on the tip end side of two or more link mechanisms among the three or more link mechanisms in the parallel link mechanism having any of the above configurations of the present invention. It is equipped with an attitude control actuator. Therefore, each effect mentioned above is acquired about the parallel link mechanism of this invention.

Any combination of at least two configurations disclosed in the claims and/or the specification and/or the drawings is included in the present invention. In particular, any combination of two or more of each claim is included in the invention.

The present invention will be more clearly understood from the following description of preferred embodiments with reference to the accompanying drawings. However, the embodiments and drawings are for illustration and description only and should not be used to define the scope of the invention. The scope of the invention is defined by the appended claims. In the accompanying drawings, the same part number in multiple drawings indicates the same or corresponding part.
It is the front view which omitted a part of parallel link mechanism concerning a 1st embodiment of the present invention. FIG. 2 is a partial cross-sectional view taken along line IIA-IIA of FIG. 1; FIG. 2B is a partially enlarged view of a portion IIB of FIG. 2A; It is the figure which represented one link mechanism of the same parallel link mechanism with a straight line. It is a longitudinal cross-sectional view of a grease-filled bearing of the parallel link mechanism. It is an evaluation result of fretting wear resistance at low surface pressure. It is an evaluation result of fretting wear resistance under high surface pressure. It is a front view of a parallel link mechanism concerning a 2nd embodiment of the present invention. It is a horizontal sectional view of the end part link member of each proximal end side of the same parallel link mechanism. It is a horizontal sectional view of the end part link member of each front end side of the same parallel link mechanism. FIG. 11 is a perspective view of a link actuating device according to a third embodiment of the invention; It is the front view of the simple model which abbreviate|omitted two link mechanisms of the same link actuation apparatus. 11 is a partial cross-sectional view along line XIA-XIA of FIG. 10; FIG. 11B is a partially enlarged view of the XIB portion of FIG. 11A; FIG. It is a figure which shows the maximum bending angle etc. of the same link actuating device.

[First embodiment]
A parallel link mechanism, which is a type of joint mechanism according to an embodiment of the present invention, will be described with reference to FIGS. 1 to 4. FIG.
As shown in FIG. 1, the parallel link mechanism (joint mechanism) 9 connects a link hub 13 on the distal end side to a link hub 12 on the proximal end side via three sets of link mechanisms 14 so that the posture can be changed. be. The number of sets of link mechanisms 14 may be four or more. 1, only one set of link mechanisms 14 is shown, and the remaining two link mechanisms are omitted.

Each link mechanism 14 has an end link member 15 on the base end side, an end link member 16 on the tip end side, and a center link member 17, and forms a four-bar linkage link mechanism consisting of four rotational pairs. The proximal and distal end link members 15, 16 are L-shaped (FIG. 2A). One end of the proximal end link member 15 is connected to the proximal link hub 12 , and one end of the distal end link member 16 is rotatably connected to the distal link hub 13 . The center link member 17 is rotatably connected to both ends of the end link members 15 and 16 on the base end side and the tip end side, respectively.

The parallel link mechanism 9 is a structure that combines two spherical link mechanisms. The central axis of each rotational pair of the link hub 12 on the proximal side and the end link member 15 on the proximal side, and each rotational pair of the end link member 15 on the proximal side and the center link member 17 intersect at the spherical link center PA on the side. Similarly, the central axis of each rotating pair of the tip-side link hub 13 and the tip-side end link member 16, and each rotating pair of the tip-side end link member 16 and the center link member 17 intersect at the spherical link center PB of .

Also, the distance between the center of the rotational pair of the link hub 12 on the proximal side and the end link member 15 on the proximal side and the spherical link center PA on the proximal side is the same. The distance between the center of the rotational pair of the end link member 15 on the proximal side and the center link member 17 and the spherical link center PA on the proximal side is the same. Similarly, the distance between the center of the rotational pair of the link hub 13 on the tip side and the end link member 16 on the tip side and the center PB of the spherical link on the tip side is the same. The distance between the center of the rotational pair of the end link member 16 and the center link member 17 on the tip side and the center PB of the spherical link on the tip side is the same. The central axes of each rotational pair of the proximal and distal end link members 15, 16 and the central link member 17 may have a crossing angle γ or may be parallel.

FIG. 2A shows a rotational pair portion T1 between the proximal side link hub 12 and the proximal side end link member 15, and a rotational pair portion T2 between the proximal side end link member 15 and the central link member 17. there is In the rotational pair portion T1, the proximal side link hub 12 and the proximal side end link member 15 correspond to "adjacent members", and in the rotational pair portion T2, the proximal side end link member 15 and the central link member 17 correspond to "adjacent members".

A rotating pair portion T3 of the end link member 16 on the tip end side and the center link member 17 shown in FIG. 3 has the same shape as the rotating pair portion T2 shown enlarged in FIG. 2B. A rotating pair portion T4 of the tip side link hub 13 and the tip side end link member 16 shown in FIG. 3 has the same shape as the rotating pair portion T1 shown enlarged in FIG. 2B. The tip-side end link member 16 and the center link member 17 shown in FIG. corresponds to "adjacent members" in the rotational pair portion T4.

Further, in FIG. 2A, the center axis O1 of each rotational pair portion T1 between the proximal side link hub 12 and the proximal side end link member 15, the proximal side end link member 15 and the central link member 17 and the central axis O2 of each rotational pair portion T2 is 90°. However, the angle α may be other than 90°.

The three sets of link mechanisms 14 have the same geometric shape. The geometrically identical shape means, as shown in FIG. A model represented by a straight line connecting parts T1, T2, T3, and T4 has a shape in which the proximal side part and the distal side part with respect to the central part of the central link member 17 are symmetrical regardless of the posture. It means that In the following description, the rotational pairs T1, T2, T3, and T4 may be referred to as the rotational pairs T1 and the like. FIG. 3 is a diagram showing a set of link mechanisms 14 represented by straight lines. The parallel link mechanism 9 of this embodiment is of a rotationally symmetrical type, and includes a proximal portion consisting of a proximal link hub 12 and a proximal end link member 15, a distal link hub 13 and a distal end. The positional relationship with the distal end portion formed by the central link member 16 is rotationally symmetrical with respect to the center line C of the central link member 17 .

A link hub 12 on the proximal side, a link hub 13 on the distal side, and three sets of link mechanisms 14 provide 2 freedoms in which the link hub 13 on the distal side is rotatable about two orthogonal axes with respect to the link hub 12 on the proximal side. A degree mechanism is configured. In other words, the link hub 13 on the distal end side can be rotated with two degrees of freedom and the posture can be freely changed with respect to the link hub 12 on the proximal end side. This two-degrees-of-freedom mechanism is compact, but allows a wide movable range of the link hub 13 on the distal side with respect to the link hub 12 on the proximal side.

For example, a straight line that passes through the center of the spherical link PA on the proximal side and perpendicularly intersects the central axis O1 (FIG. 2A) of the rotational pair of the link hub 12 on the proximal side and the end link member 15 on the proximal side is , the central axis QA of the link hub 12. Similarly, a straight line that passes through the center PB of the spherical link on the tip side and perpendicularly intersects the central axis O1 (FIG. 2A) of the rotational pair of the link hub 13 on the tip side and the end link member 16 on the tip side is defined as the link hub on the tip side. 13 as the central axis QB.

In this case, the maximum bending angle θmax, which is the maximum bending angle θ between the central axis QA of the link hub 12 on the proximal side and the central axis QB of the link hub 13 on the distal side, can be about ±90°. Further, the turning angle φ of the link hub 13 on the distal side with respect to the link hub 12 on the proximal side can be set within a range of 0° to 360°. The bending angle θ is a vertical angle at which the central axis QB of the link hub 13 on the distal end side is inclined with respect to the central axis QA of the link hub 12 on the proximal side. The turning angle φ is a horizontal angle at which the central axis QB of the link hub 13 on the distal side is inclined with respect to the central axis QA of the link hub 12 on the proximal side. Note that the maximum bending angle θmax may be 90° or more.

The posture of the link hub 13 on the front end side relative to the link hub 12 on the base end side is changed with the intersection point O of the center axis QA of the link hub 12 on the base end side and the center axis QB of the link hub 13 on the front end side as the center of rotation. will be FIG. 1 shows a state in which the central axis QA of the link hub 12 on the base end side and the central axis QB of the link hub 13 on the distal end side are on the same line, and FIG. It shows a state where an operating angle (bent angle) is taken. Even if the attitude of the link hub 13 on the front end side with respect to the link hub 12 on the base end side changes, the distance L between the spherical link centers PA and PB on the base end side and the front end side does not change.

As shown in FIG. 1, the link hub 12 on the proximal side includes a flat plate-shaped proximal member 6 and three rotating shaft connecting members 21 (FIG. 2A) provided integrally with the proximal member 6. have. The base end member 6 shown in FIG. 2A has a circular through hole 6a in the central portion, and three rotating shaft connecting members 21 are arranged at equal intervals in the circumferential direction around this through hole 6a. The center of the through hole 6a is located on the center axis QA (Fig. 1) of the link hub 12 on the base end side.

A bearing 23 is provided on each rotating pair T1 and the like. As shown in FIG. 2B, in the rotation pair portion T1 between the link hub 12 (FIG. 2A) on the base end side and the end link member 15 on the base end side, the rotation shaft is connected to each of the rotation shaft connecting members 21 via the bearing 23. 22 are rotatably connected. The axis of this rotating shaft 22 intersects with the center axis QA (FIG. 1) of the link hub 12 on the base end side. One end of the proximal end link member 15 is connected to the rotating shaft 22 so as to rotate together with the rotating shaft 22 .

The rotary shaft 22 has a large-diameter portion, a small-diameter portion, and a male threaded portion in order along the axial direction, and is rotatably supported by the rotary shaft connecting member 21 via two bearings 23 at the small-diameter portion. there is The outer peripheral surfaces of the two bearings 23 are fitted in an inner diameter groove provided in the rotating shaft connecting member 21 and fixed. The types and installation methods of the bearings provided in the other rotating pairs T2, T3, and T4 (FIG. 3) are substantially the same.

A cutout portion 25 is formed at one end of the end link member 15 on the base end side, and both side portions of the cutout portion 25 constitute a pair of inner and outer rotating shaft support portions 27 and 26 . A through hole is formed in each of the pair of rotating shaft support portions 27 and 26 . The rotating shaft connecting member 21 is arranged in the notch portion 25 , and the small diameter portion of the rotating shaft 22 is inserted through the through hole and the inner peripheral surface of the inner ring of the bearing 23 . The male threaded portion of the rotary shaft 22 protrudes inward (lower in FIG. 2B) than the rotary shaft support portion 27 on the inner side. A nut Nt is screwed onto the male threaded portion. A spacer Sp is interposed between the inner rotating shaft support portion 27 and the inner ring end face facing this rotating shaft supporting portion 27, and the outer rotating shaft supporting portion 26 and this rotating shaft supporting portion 26 are opposed to each other. A spacer Sp is interposed between the two inner ring end faces. Therefore, preload is applied to the bearing 23 when the nut Nt is screwed.

A rotation shaft 22 is connected to one end of the central link member 17 via a bearing 23 to the rotational pair portion T2 of the end link member 15 on the base end side and the central link member 17 . That is, a rotating shaft 22 rotatably connected to one end of a central link member 17 is connected to the other end of the end link member 15 on the base end side. The rotary shaft 22 is rotatably supported at one end of the central link member 17 via two bearings 23 at the small diameter portion. A cutout portion 37 is formed at the other end of the end link member 15 on the base end side, and both side portions of the cutout portion 37 constitute a pair of inner and outer rotary shaft support portions 39 and 38 . A through hole is formed in each of the pair of rotating shaft support portions 39 and 38 .

One end of the central link member 17 is arranged in the notch portion 37 , and the small diameter portion is inserted through the through hole and the inner ring inner peripheral surface of the bearing 23 . Furthermore, a nut Nt is screwed onto the male threaded portion of the rotary shaft 22 . Spacers Sp, Sp are interposed between the inner ring end surface of the bearing 23 and the pair of rotating shaft support portions 39, 38, and preload is applied to the bearing 23 when the nut Nt is screwed.

As shown in FIG. 1, the link hub 13 on the front end side has a flat tip member 40 and three rotating shaft connecting members 41 provided on the bottom surface of the tip member 40 at equal intervals in the circumferential direction. . The center of the circumference where each rotating shaft coupling member 41 is arranged is positioned on the central axis QB of the link hub 13 on the tip side. A rotating shaft 22 whose axis intersects the center axis QB of the link hub 13 on the distal end side is rotatably connected to each rotating shaft connecting member 41 . One end of an end link member 16 on the tip side is connected to the rotating shaft 22 . The other end of the end link member 16 on the tip side is connected to a rotating shaft 22 that is rotatably connected to the other end of the central link member 17 .

Through two bearings 23 (FIG. 4) provided on each rotating shaft connecting member 41, the rotating pair T4 (FIG. 3) of the link hub 13 on the tip end side and the end link member 16 on the tip end side, A rotating shaft 22 is rotatably connected. A rotating shaft T3 (FIG. 3) between the end link member 16 on the distal end side and the central link member 17 is provided with two bearings 23 (FIG. 4) provided at the other end of the central link member 17. 22 are rotatably connected.

<Grease filled bearing>
As shown in FIG. 4, the bearing 23 is a grease-filled bearing, comprising an inner ring 2 and an outer ring 3 which are bearing rings, a plurality of rolling elements 4 interposed between the inner and outer rings 2 and 3, and these rolling elements 4. It comprises a retainer 5 for holding, a seal member 6 for sealing a bearing space between the inner and outer rings 2 and 3, and a grease composition gr, which will be described later, sealed in the bearing space. The grease-filled bearing of this example is an angular contact ball bearing, and steel balls, for example, are applied as the rolling elements 4 . The angular contact ball bearing of this embodiment is a combination angular contact ball bearing used in a back-to-back manner. The duplex angular contact ball bearing has a seal member 6 on the axial outer surface opposite to the mating surface. In other words, in this combination angular contact ball bearing, no seal member is provided on the axially inner surface, which is the mating surface side, and the seal member 6 is provided only on the axially outer surface. The opposite mating surface side is sometimes referred to as the front side.

An outer ring seal mounting groove 3a for fitting and fixing the seal member 6 is formed on the inner peripheral surface of the outer ring 3 on the front side. The seal member 6 is a so-called non-contact seal, and has a base end attached to the outer ring seal mounting groove 3a and a tip end having a seal lip inserted into the inner ring seal groove 2a without contact. The seal member 6 may be a contact seal in which a seal lip contacts the inner ring seal groove or the outer peripheral surface of the inner ring. In addition, the sealing member can also be configured by a shield plate made of only a steel plate.

<Regarding grease composition gr>
The grease composition gr contains a base oil and a thickener, has a worked penetration of 310 or more, and the thickener is a calcium sulfonate complex soap. The calcium sulfonate complex soap of this embodiment is a complex soap obtained by combining calcium sulfonate and a calcium salt other than calcium sulfonate. The thickener of the grease composition is only the calcium sulfonate complex soap, and it is preferable that other metal soaps, urea compounds, and the like are not included as thickeners. As a result, the ionic interaction of the calcium salt portion is not affected by other components, the properties of the grease are stable over a long period of time, and a drop in consistency is less likely to occur. Therefore, it contributes to good sealing performance.

Examples of calcium sulfonates include dodecylbenzenesulfonic acid, octadecylbenzenesulfonic acid, dilaurylcetylbenzenesulfonic acid, dinonylnaphthalenesulfonic acid, paraffin wax-substituted benzenesulfonic acid, polyolefin-substituted benzenesulfonic acid, and polyisobutylene-substituted benzenesulfonic acid. Calcium salts of alkylaromatic sulfonic acids, calcium salts of aromatic sulfonic acids, calcium salts of alkylsulfonic acids, calcium salts of petroleum sulfonic acids, and the like.

Examples of calcium salts other than calcium sulfonate include calcium salts of inorganic acids such as carbonic acid, boric acid, phosphoric acid, hydrochloric acid, and sulfonic acid, behenic acid, arachidic acid, stearic acid, hydroxystearic acid, hexadecanoic acid, and octanoic acid. calcium salts of higher fatty acids, calcium salts of lower fatty acids such as acetic acid, butyric acid and valeric acid, and calcium salts of inorganic bases. Also included are calcium salts of dibasic fatty acids such as, for example, azelaic acid, sebacic acid, adipic acid, glutaric acid, succinic acid, malonic acid, and oxalic acid. Calcium salts other than calcium sulfonate may be used singly or in combination of two or more.

The calcium sulfonate complex soap may be synthesized in advance and dispersed in the base oil, or may be synthesized in the base oil and dispersed in the base oil. The latter method is preferable because the manufacturing process can be simplified and the thickener can be well dispersed in the base oil.

When synthesizing calcium sulfonate complex soap in base oil, for example, water, calcium hydroxide, higher fatty acid, lower fatty acid, inorganic acid, etc. are added to alkylaromatic sulfonic acid dispersed in base oil, and the mixture is heated and stirred. , heating and removing water to obtain a calcium sulfonate complex soap.

The base oil used in the grease composition can be used without any particular limitation as long as it is usually used for rolling bearings. Examples thereof include mineral oils such as paraffinic mineral oils and naphthenic mineral oils, synthetic hydrocarbon oils such as PAO oils and alkylbenzene oils, ester oils, ether oils, silicone oils, and fluorine oils. These base oils may be used alone or in combination of two or more.

The combination of base oil and thickener is related to the interaction between the thickeners in the base oil and affects the thickening effect. Therefore, it is preferable to select an appropriate combination. For the calcium sulfonate complex soap used in this embodiment, the base oil is preferably mineral oil or synthetic hydrocarbon oil. From a cost point of view, the base oil is preferably mineral oil. Moreover, from the viewpoint of lubricating performance at high temperatures, the base oil is preferably a synthetic hydrocarbon oil.

As the mineral oil, paraffinic mineral oil is preferable from the viewpoint of lubricity, and naphthenic mineral oil is preferable from the viewpoint of cost. The mineral oil can be refined by appropriately combining vacuum distillation, solvent deasphalting, solvent extraction, hydrocracking, solvent dewaxing, sulfuric acid washing, clay refining, hydrorefining, and the like.

PAO oil (polyalphaolefin oil) is more preferable as the synthetic hydrocarbon oil. PAO oils are mixtures of alpha-olefins or isomerized alpha-olefin oligomers or polymers. Specific examples of α-olefins include 1-octene, 1-nonene, 1-decene, 1-dodecene, 1-tridecene, 1-tetradecene, 1-pentadecene, 1-hexadecene, 1-heptadecene, 1-octadecene, 1 -nonadecene, 1-eicosene, 1-docosene, 1-tetradocosene and the like, and mixtures thereof are usually used.

The kinematic viscosity of the base oil (in the case of a mixed oil, the kinematic viscosity of the mixed oil) is preferably 10 to 200 mm ² /s at 40°C. It is more preferably 10 to 100 mm ² /s, still more preferably 30 to 100 mm ² /s.

The grease composition gr may further contain other additives as long as the object of the present invention is not impaired. Examples of additives include amine, phenol, and sulfur antioxidants, chlorine, sulfur, and phosphorus compounds, extreme pressure agents such as organic molybdenum, sulfonates, polyhydric alcohol esters, and sorbitan esters. Rust preventives such as, esters, oily agents such as alcohol, and the like. The grease-filled bearing of this embodiment is mainly used under high load conditions. Therefore, it is preferable to contain an extreme pressure agent. When additives are added, the content of the additives as a whole is preferably 5% by mass or less with respect to the entire grease composition.

　Calcium sulfonate complex soap not only has a thickening effect when blended with the base oil, but also has a rust-preventing effect that makes it difficult for metals in contact with it to rust. Therefore, the calcium sulfonate complex soap can serve as both a thickener and an antirust agent. Therefore, the grease does not need to contain a separate rust preventive agent.

The worked penetration of the grease composition gr is 310 or more. By setting the worked penetration within this range, the inflow of grease to the contact portion between the rolling elements 4 and the bearing ring is improved, and the fretting wear resistance is excellent. The worked penetration of the grease composition gr is more preferably 310-340. Within this range, the fluidity of the grease is restricted to a predetermined range, and the sealing performance is excellent.

In the grease-filled bearing of this embodiment, the grease thickener is a calcium sulfonate composite soap. Therefore, a thickener film that can withstand a high load is formed. As a result, this grease-filled bearing can be used under high load conditions in which the maximum contact surface pressure on the bearing ring is 2000 MPa or more and under conditions of less than the critical rocking angle. Therefore, grease-filled bearings can be applied to applications requiring high precision, where fretting wear is likely to occur in general-purpose deep groove ball bearings. The maximum contact surface pressure of the bearing ring is more preferably 2300 MPa or more, further preferably 2700 MPa or more.

The critical swing angle when the grease-filled bearing is an angular contact ball bearing is expressed by the following relationship in the case of inner ring swing.
Critical swing angle = (360°/Z) (Dpw/(Dpw-DwCOSα1))
In the above formula, Z is the number of balls per row of the single-row angular contact ball bearing, Dpw is the pitch circle diameter of the balls, Dw is the diameter of the balls, and α1 is the contact angle. In the case of outer ring oscillation, the denominator on the right side is Dpw+DwCOSα1.

<Effect>
According to the parallel link mechanism 9 described above, the link hub 12 on the proximal side, the link hub 13 on the distal side, and the three or more sets of link mechanisms 14 are configured to connect the link hub 13 on the distal side to the link hub 12 on the proximal side. constitutes a two-degree-of-freedom mechanism that is rotatable around two orthogonal axes. In other words, the posture of the link hub 13 on the distal end side can be changed with two degrees of freedom in rotation relative to the link hub 12 on the proximal end side. This two-degrees-of-freedom mechanism is compact, but allows a wide movable range of the link hub 13 on the distal side with respect to the link hub 12 on the proximal side.

The parallel link mechanism 9 performs a swinging motion in which each rotating pair portion is in the vicinity of ±θmax/2 with respect to the maximum bending angle θmax, which is the operating range. The revolving motion of the rolling elements 4 is 1/2 of the rocking motion of the rotating pair. Further, the rigidity of the parallel link mechanism 9 largely contributes to the moment rigidity of the bearing 23, and the bearing 23 is often used in a high preload state. A grease-encapsulated bearing in which the following grease composition gr is enclosed is applied to the rotating pair portion of the parallel link mechanism 9 as described above. The grease composition gr contains a base oil and a thickener, has a worked penetration of 310 or more, and the thickener is a calcium sulfonate complex soap. As a result, the inflow of grease to the contact portion between the rolling elements 4 and the bearing ring is improved, and the fretting wear resistance is excellent. Further, if a grease-filled bearing is used in the rotating pair portion, even if the bearing 23 is slightly oscillated in a high preload state, catching during subsequent rotation is reduced and high-speed operation becomes possible. Therefore, it is possible to realize the parallel link mechanism 9 that is capable of high-speed operation over a wide operating range, and that realizes a long life and smooth movement.

The rigidity of the parallel link mechanism 9 greatly contributes to the moment rigidity of the bearing 23. Therefore, by using a back-to-back combination angular contact ball bearing as the bearing 23 applied to the rotating pair portion, the moment rigidity of the bearing 23 can be increased with an inexpensive bearing structure. As a result, the rigidity of the parallel link mechanism 9 can be increased and the cost can be reduced.

When the paired angular contact ball bearing is provided with a seal member 6 on the axial outer surface opposite to the mating surface, the minimum number of parts is required to prevent foreign matter from entering the bearing 23 and grease leakage from the bearing 23. can. Also, the orientation of the bearings 23 installed when the parallel link mechanism 9 is assembled can be easily determined by the presence or absence of the seal member 6 . Therefore, assemblability is improved, leading to cost reduction.

<About other embodiments>
In the following description, the same reference numerals are given to the parts corresponding to the items previously described in each embodiment, and redundant description is omitted. When only a portion of the configuration is described, the other portions of the configuration are the same as those previously described unless otherwise specified. The same configuration has the same effect. It is possible not only to combine the parts specifically described in each embodiment, but also to partially combine the embodiments if there is no problem with the combination.

[Second Embodiment: FIGS. 6 to 8]
In the parallel link mechanism 9 shown in FIG. 6, the arm length L2A on the proximal end side and the arm length L2B on the distal end side are different. 7 is a partial cross-sectional view taken along line VII-VII of FIG. 6. FIG. 8 is a partial cross-sectional view taken along line VIII-VIII of FIG. 6. FIG. As shown in FIG. 6, the distance from the center PA of the spherical link on the proximal side to the center point C1A (FIG. 7) of each rotation pair between the end link member 15 and the central link member 17 on the proximal side (hereinafter referred to as "link L1A (FIG. 7) are identical to each other. Similarly, the distance (hereinafter referred to as "link length") L1B from the center PB of the spherical link on the tip side to the center point C1B (FIG. 8) of each rotational pair between the end link member 16 and the center link member 17 on the tip side (FIG. 8) are identical to each other. The link length L1A on the proximal end side and the link length L1B on the distal end side are the same.

On the other hand, the distance from the base end spherical link center PA to each rotation pair center point C2A (FIG. 7) between the base end link hub 12 and the base end link member 15 (hereinafter referred to as "arm ) is L2A. Similarly, the distance from the center PB of the spherical link on the tip side to the center point C2B (FIG. 8) of the link hub 13 on the tip side and the end link member 16 on the tip side (hereinafter referred to as "arm length") ) is L2B. The link length L2A on the proximal end side and the link length L2B on the distal end side are different. In this embodiment, the proximal arm length L2A is longer than the distal arm length L2B (L2A>L2B).

Here, the rotational pair center points C1A (FIG. 7), C1B (FIG. 8), C2A (FIG. 7), and C2B (FIG. 8) are the edges along the rotational pair axes O1A, O1B, O2A, and O2B in each rotational pair portion. It indicates the central point of the width direction of the partial link members 15 and 16 .

The parallel link mechanism 9 has an arm length L2A on the proximal end side and an arm length L2B on the distal end side. Therefore, the degree of freedom in design is increased, and design changes for expanding the movable range and reducing the weight of the distal end are facilitated. Even if the arm length L2A on the proximal side and the arm length L2B on the distal side are different, if the proximal side and the distal side have the same shape geometrically, the distal end of the link hub 12 on the proximal side is A two-degrees-of-freedom mechanism is configured in which the side link hub 13 can change its posture with two degrees of freedom in rotation.

As in this embodiment, when the arm length L2B on the distal end side is shorter than the arm length L2A on the proximal end side, the constituent parts of the parallel link mechanism 9 are less likely to interfere with each other, and a compact configuration can have a wide movable range. In addition, since the weight of the tip side can be reduced, the moment of inertia of the tip side becomes small, and high-speed operation becomes possible. Other effects similar to those of the above-described embodiment are obtained.

<Link actuating device (third embodiment): FIGS. 9 to 12>
As shown in FIG. 9, the link actuating device 7 can arbitrarily change the attitude of the parallel link mechanism 9 according to any one of the first and second embodiments and the link hub 13 on the distal end side of the parallel link mechanism 9. and an attitude control actuator 10 to control.

<Attitude control actuator>
The attitude control actuator 10 is a rotary actuator provided with a speed reduction mechanism 52 shown in FIG. ing. The attitude control actuator 10 is provided integrally with a speed reduction mechanism 52 , and the speed reduction mechanism 52 is fixed to the base end member 6 ( FIG. 10 ) by a motor fixing member 53 . The attitude control actuator 10 may be equipped with a brake.

In this example, as shown in FIG. 11A, all three sets of link mechanisms 14 are provided with attitude control actuators 10, but at least two of the three sets of link mechanisms 14 are provided with attitude control actuators 10. If provided, the posture of the link hub 13 on the distal side with respect to the link hub 12 on the proximal side can be determined.

As shown in FIG. 10, the link actuating device 7 actuates the parallel link mechanism 9 by rotationally driving each attitude control actuator 10 . Specifically, when the attitude control actuator 10 is rotationally driven, the rotation is decelerated and transmitted to the rotating shaft 22 via the deceleration mechanism 52 shown in FIG. 11B. As a result, as shown in FIG. 12, the posture of the link hub 13 on the distal side with respect to the link hub 12 on the proximal side is arbitrarily changed. An end effector (not shown) is attached to the tip member 40 of the link hub 13 on the tip side. Examples of end effectors include hands including grippers, cleaning nozzles, dispensers, welding torches, image processing equipment, and the like.

This link actuating device 7 is capable of performing fine movements at high speed. Therefore, in many cases, the operation-stop-work with the end effector is frequently repeated, and each time the acceleration and deceleration applied to the bearing 23 shown in FIG. Slippage is increasing.

In addition, each rotating pair performs a swinging motion in the vicinity of ±θmax/2 [deg] with respect to the maximum bending angle θmax [deg], which is the operating range of the link actuating device 7 shown in FIG. 12 . Therefore, the link actuating device 7 has a swing angle of the rotating pair smaller than that of a general robot. Further, the rigidity of the link actuating device 7 largely contributes to the moment rigidity of the bearing, and the bearing 23 is often used in a high preload state. By applying the grease-encapsulated bearing in which the above-described grease composition is encapsulated to the rotating pair portion, the fretting wear resistance is excellent.

In addition, if the grease-filled bearing is used in the rotating mating part, even if the bearing 23 is slightly oscillated in a high preload state, the catching during subsequent rotation is reduced and high-speed operation is possible. Therefore, it is possible to realize the link actuating device 7 that is capable of high-speed operation in a wide operating range and that achieves a long life and smooth movement.

The thickener of the grease-filled bearing may be lithium soap, as shown in the examples described later. In this case, although the sealing performance is inferior to that of the grease-encapsulated bearing in which the thickener is a calcium sulfonate complex soap, it has sufficient fretting wear resistance. It is also possible to use a combined angular contact ball bearing in which the angular contact ball bearings are face-to-face. The grease-filled bearings may be deep groove ball bearings or cross roller bearings instead of angular ball bearings. The grease-filled bearing of the present invention may be adopted only for some of the rotating pair portions.

A grease-encapsulated bearing containing the grease composition described above may be applied to the joint mechanism of a vertical articulated robot or a horizontal articulated robot.

The present invention will be described in more detail below with reference to examples, but the present invention is not limited by these examples.

Seven types of grease compositions having the compositions shown in Table 1 were prepared. In the grease compositions of Examples 1 and 2, the thickener is a calcium sulfonate complex soap, and the worked penetration is NLGI No. 1 (310 to 340). The grease composition of Example 3 contains lithium soap as a thickener and has a worked penetration of NLGI No. 0 (355 to 385).

(1) Fretting wear resistance test A Fafner type micro-movement wear test was performed on a combined angular contact ball bearing in which sealed angular contact ball bearings were aligned back to back, that is, a DB set of sealed angular contact ball bearings, and the fretting wear resistance of each of the above seven types of grease was tested. evaluated the sex. The test conditions conformed to ASTM D4170. Specifically, the amount of grease was 1±0.05 g, the motor was rotated in the atmosphere at room temperature, and the test was conducted under the conditions of a swing angle of 12 degrees and a swing cycle of 30 Hz. The fretting wear resistance was evaluated based on the amount of decrease in mass of the bearing ring after the test (hereinafter referred to as "amount of wear").

The load conditions were evaluated according to the following two levels. The first condition is a contact surface pressure of 1700 MPa in accordance with ASTM D 4170 (hereinafter referred to as "low surface pressure"). The second condition assumed a high moment load and set the contact surface pressure to 3000 MPa (hereinafter referred to as "high surface pressure").

　Fretting wear resistance test results are shown in Figures 5A and 5B and Table 1. 5A and 5B show the relationship between the amount of wear and the worked penetration obtained in tests using three samples for each grease. FIG. 5A shows the results under low surface pressure conditions, and FIG. 5B shows the results under high surface pressure conditions. The reference line represented by the dotted line in FIGS. 5A and 5B was determined based on grease that does not cause fretting wear under actual use conditions (under conditions where the bearing rotation direction changes and oscillates with acceleration/deceleration).

In the columns of low surface pressure and high surface pressure of the Fafner test wear amount in Table 1, the average value of the wear amount of the three samples under each condition is greater than a predetermined value. The fretting wear results are described.
〇: Below reference line ×: Above reference line

(2) Bearing sealing property test A bearing rocking test was performed at less than the critical rocking angle (critical rocking angle is 44.8 degrees) for the sealed angular contact ball bearing DB set (bearing inner diameter 6 mm) filled with the above 7 types of grease. Three samples were used, and the presence or absence of grease leakage was visually confirmed. The bearing sealing property was judged by whether or not the leakage of grease could be confirmed from the appearance of the bearing after the bearing rocking test was carried out. In this case, it was judged that the bearing sealing property was good when there was no grease leakage from all bearings, and the bearing sealing property was judged to be poor when there was grease leakage from one or more bearings.

From the results of FIGS. 5A and 5B, it can be seen that the higher the worked penetration value, the lower the wear amount and the better the fretting wear resistance. In addition, when the load condition is a high surface pressure condition, the amount of wear tends to increase overall compared to the case of a low surface pressure condition. The amount of wear in Examples 1, 2, and 3 was relatively low even under high surface pressure conditions. In addition, grease with a worked penetration of 310 or more resulted in a low wear amount and excellent fretting wear resistance.

In addition, in Example 1, Example 2, Comparative Example 1, Comparative Example 2, and Reference Proposal Example 2, no grease leakage was confirmed, and the worked penetration was NLGI No. 2 (265 to 295) or increased penetration. It was found that grease containing calcium sulfonate complex soap as an agent has good bearing sealing properties.

Comparing Example 2 and Reference Proposal Example 1, both base oils are synthetic hydrocarbon oils and the worked penetration is the same, but Reference Proposal Example 1 containing a urea compound as a thickener is a calcium sulfonate composite The sealing performance was inferior to that of Example 2 containing soap. Calcium sulfonate complex soaps as thickeners are known to have low thixotropy when subjected to shear stress and small changes in grease consistency (Non-Patent Document 1). Therefore, by using a calcium sulfonate complex soap as a thickener, the change in grease consistency during operation is smaller than when using other thickeners, and the worked penetration during non-operation is relatively high. It is considered that even at the level, good sealing performance was exhibited.

From the above, when the results of the fretting wear resistance and bearing sealing performance tests are summarized, Examples 1 and 2 showed good results in both fretting wear resistance and sealing performance. From these results, it was found that using a calcium sulfonate complex soap as a thickener, containing a mineral oil or a synthetic hydrocarbon oil as a base oil, and having a worked penetration of 310 to 340 makes it possible to achieve both fretting wear resistance and sealing performance. It can be said that it is effective for

<Reference Proposal Example 1>
According to Reference Proposal Example 1 of the above embodiment, it is possible to apply a "urea compound" as a thickening agent to a grease-filled bearing in a parallel link mechanism. In this case, although the sealing properties are inferior to those of Examples 1 and 2 containing the calcium sulfonate complex soap, the fretting wear resistance at low surface pressure is excellent.

The parallel link mechanism according to this reference proposal example 1 is described as follows.
A link hub on the distal end side is connected to a link hub on the proximal side via three or more sets of link mechanisms so as to be able to change their attitudes, and one end of each of the link mechanisms is rotatable with respect to the link hub on the proximal side. A proximal side end link member connected, a distal side end link member having one end rotatably connected to the distal side link hub, and these proximal side and distal side end link members. a central link member having both ends rotatably connected to the other end,
A rotational pair portion between the proximal link hub and the proximal end link member, a rotational pair portion between the proximal end link member and the central link member, and the distal end link. A bearing is provided at each rotational pair portion including a rotational pair portion between the member and the central link member and a rotational pair portion between the tip side link hub and the tip side end link member, and a plurality of the bearings at least one bearing in is a grease-filled bearing comprising inner and outer rings that are bearing rings, a plurality of rolling elements interposed between the inner and outer rings, and a grease composition sealed in the bearing space between the inner and outer rings A parallel link mechanism,
The grease composition contains a base oil and a thickener and has a worked penetration of 310 or more,
The parallel link mechanism, wherein the thickener is a urea compound.

<Reference Proposal Example 2>
From Reference Proposal Example 2 of the above embodiment, it is conceivable that in the parallel link mechanism, the mixed penetration of the grease composition of the grease-filled bearing is 265 or more and 295 or less, and a "urea compound" is applied as a thickener. . In this case, although the fretting wear resistance at high surface pressure is inferior, the fretting wear resistance at low surface pressure is excellent and the sealing performance is excellent.

The parallel link mechanism according to the reference proposal example 2 is described as follows.
A link hub on the distal end side is connected to a link hub on the proximal side via three or more sets of link mechanisms so as to be able to change their attitudes, and one end of each of the link mechanisms is rotatable with respect to the link hub on the proximal side. A proximal side end link member connected, a distal side end link member having one end rotatably connected to the distal side link hub, and these proximal side and distal side end link members. a central link member having both ends rotatably connected to the other end,
A rotational pair portion between the proximal link hub and the proximal end link member, a rotational pair portion between the proximal end link member and the central link member, and the distal end link. A bearing is provided at each rotational pair portion including a rotational pair portion between the member and the central link member and a rotational pair portion between the tip side link hub and the tip side end link member, and a plurality of the bearings at least one bearing in is a grease-filled bearing comprising inner and outer rings that are bearing rings, a plurality of rolling elements interposed between the inner and outer rings, and a grease composition sealed in the bearing space between the inner and outer rings A parallel link mechanism,
The parallel link mechanism, wherein the grease composition contains a base oil and a thickener, has a worked penetration of 265 or more and 295 or less, and the thickener is a urea compound.

The present invention is not limited to the above embodiments, and various additions, changes, or deletions are possible without departing from the scope of the present invention. Accordingly, such are also included within the scope of this invention.

2... Inner ring 3... Outer ring 4... Rolling element 6... Seal member 9... Parallel link mechanism (joint mechanism)
REFERENCE SIGNS LIST 10: attitude control actuator 12: proximal link hub 13: distal link hub 14: link mechanism 15: proximal end link member 16: distal end link member 17: central link member 23 ... Bearing gr ... Grease composition

Claims (11)

1. A joint mechanism in which adjacent members are rotatably connected via a rotating pair, and a grease-filled bearing in which a grease composition is sealed is provided in the rotating pair,
   The grease composition contains a base oil and a thickener and has a worked penetration of 310 or more,
   A joint mechanism, wherein the thickening agent is calcium sulfonate complex soap or lithium soap.
2. A link hub on the distal end side is connected to a link hub on the proximal side via three or more sets of link mechanisms so as to be able to change their attitudes, and one end of each of the link mechanisms is rotatable with respect to the link hub on the proximal side. A proximal side end link member connected, a distal side end link member having one end rotatably connected to the distal side link hub, and these proximal side and distal side end link members. a central link member having both ends rotatably connected to the other end,
   A rotational pair portion between the proximal link hub and the proximal end link member, a rotational pair portion between the proximal end link member and the central link member, and the distal end link. A bearing is provided at each rotational pair portion including a rotational pair portion between the member and the central link member, and a rotational pair portion between the link hub on the tip side and the end link member on the tip side, and in the plurality of bearings At least one bearing is a grease-filled bearing comprising inner and outer rings, which are bearing rings, a plurality of rolling elements interposed between the inner and outer rings, and a grease composition sealed in a bearing space between the inner and outer rings. A parallel link mechanism,
   The grease composition contains a base oil and a thickener and has a worked penetration of 310 or more,
   The parallel link mechanism, wherein the thickener is calcium sulfonate complex soap or lithium soap.
3. The parallel link mechanism according to claim 2, wherein the grease-filled bearing is used under a high load condition in which the maximum contact surface pressure on the bearing ring is 2000 MPa or more and under a condition of less than the critical swing angle.
4. The parallel link mechanism according to claim 2 or claim 3, wherein the grease composition has a calcium sulfonate complex soap as the thickener and a worked penetration of 310-340.
5. The parallel link mechanism according to any one of claims 2 to 4, wherein the base oil of the grease composition is mineral oil or synthetic hydrocarbon oil.
6. The parallel link mechanism according to any one of claims 2 to 5, wherein the grease-filled bearing is an angular contact ball bearing.
7. A parallel link mechanism according to claim 6, wherein said angular contact ball bearing is a combination angular contact ball bearing used back to back.
8. The parallel link mechanism according to claim 7, wherein the paired angular contact ball bearing has a sealing member on the axial outer surface opposite to the mating surface.
9. In the parallel link mechanism according to any one of claims 2 to 8, two or more link mechanisms among the three or more link mechanisms are configured to arbitrarily control the attitude of the link hub on the tip end side. A link actuator with a control actuator.
10. A link hub on the distal end side is connected to a link hub on the proximal side via three or more sets of link mechanisms so as to be able to change their attitudes, and one end of each of the link mechanisms is rotatable with respect to the link hub on the proximal side. A proximal side end link member connected, a distal side end link member having one end rotatably connected to the distal side link hub, and these proximal side and distal side end link members. A grease composition for use in a parallel link mechanism having a central link member rotatably connected at both ends to the other end,
    The grease composition contains a base oil and a thickener and has a worked penetration of 310 or more,
    The grease composition, wherein the thickener is calcium sulfonate complex soap or lithium soap.
11. A link hub on the distal end side is connected to a link hub on the proximal side via three or more sets of link mechanisms so as to be able to change their attitudes, and one end of each of the link mechanisms is rotatable with respect to the link hub on the proximal side. A proximal side end link member connected, a distal side end link member having one end rotatably connected to the distal side link hub, and these proximal side and distal side end link members. A bearing used in a parallel link mechanism having a central link member with both ends rotatably connected to the other end,
    The bearing includes a rotational pair portion between the proximal side link hub and the proximal side end link member, a rotational pair portion between the proximal side end link member and the central link member, and the distal end side. provided in each rotational pair portion including a rotational pair portion between the end link member and the central link member, and a rotational pair portion between the tip side link hub and the tip side end link member, and a plurality of At least one of the bearings includes inner and outer rings as bearing rings, a plurality of rolling elements interposed between the inner and outer rings, and a grease composition sealed in a bearing space between the inner and outer rings. a bearing,
    The grease composition contains a base oil and a thickener and has a worked penetration of 310 or more,
    The thickener is calcium sulfonate complex soap or lithium soap,
    bearing.

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