Parallel link mechanism, constant velocity universal joint, and link actuator

1. A parallel link mechanism comprising:

a proximal end side link hub;

a distal end side link hub; and

three or more link mechanisms that connect the distal end side link hub to the proximal end side link hub in a position-changeable fashion,

each of the link mechanisms having a trinodal structure with four revolute pairs, and including a proximal side end link member, one end of the proximal side end link member being pivotably connected to the proximal end side link hub; a distal side end link member, one end of the distal side end link member being pivotably connected to the distal end side link hub; and an intermediate link member which is pivotably connected to the other ends of the proximal side end link member and the distal side end link member, and

each of the link mechanisms having such a shape that a geometric model of the link mechanism represented by lines shows symmetry between a proximal end side portion thereof and a distal end side portion thereof with respect to a center portion of the intermediate link member,

wherein each revolute pair of each of the link mechanisms includes one pair of pair constituent members connected to each other via a bearing,

wherein one of the pair constituent members is formed with a shaft portion fitted to an inner periphery of an inner ring of the bearing, and the other of the pair constituent members is formed with an annular inner face forming portion fitted to an outer periphery of an outer ring of the bearing,

wherein the shaft portion has a part formed as a stepped portion having an outer diameter greater than that of a portion of the shaft portion that is fitted to the inner periphery of the inner ring of the bearing, and having a stepped surface configured to abut against an end face of the inner ring to axially position the inner ring,

wherein the annular inner face forming portion has a part formed as a stepped portion having an inner diameter smaller than that of a portion of the annular inner face forming portion that is fitted to the outer periphery of the outer ring of the bearing, and having a stepped surface configured to abut against an end face of the outer ring to axially position the outer ring, and

wherein the shaft portion and the annular inner face forming portion cooperatively define a first sealing structure to regulate a flow of a lubricant between inside and outside of the bearing, the first sealing structure being defined in the form of a gap between an outer peripheral face of the stepped portion of the shaft portion and an inner peripheral face of the stepped portion of the annular inner face forming portion.

2. A parallel link mechanism comprising:

a proximal end side link hub;

a distal end side link hub; and

three or more link mechanisms that connect the distal end side link hub to the proximal end side link hub in a position-changeable fashion,

each of the link mechanisms having a trinodal structure with four revolute pairs, and including a proximal side end link member, one end of the proximal side end link member being pivotably connected to the proximal end side link hub; a distal side end link member, one end of the distal side end link member being pivotably connected to the distal end side link hub; and an intermediate link member which is pivotably connected to the other ends of the proximal side end link member and the distal side end link member, and

each of the link mechanisms having such a shape that a geometric model of the link mechanism represented by lines shows symmetry between a proximal end side portion thereof and a distal end side portion thereof with respect to a center portion of the intermediate link member,

wherein each revolute pair of each of the link mechanisms includes one pair of pair constituent members connected to each other via a bearing,

wherein one of the pair constituent members is formed with a shaft portion fitted to an inner periphery of an inner ring of the bearing, and the other of the pair constituent members is formed with an annular inner face forming portion fitted to an outer periphery of an outer ring of the bearing, the shaft portion and the annular inner face forming portion cooperatively define a first sealing structure to regulate a flow of a lubricant between inside and outside of the bearing,

further comprising an inner ring fixation element to fix an axial position of the inner ring of the bearing, and a spacer member interposed between the inner ring fixation element and the inner ring of the bearing, wherein the spacer member and the annular inner face forming portion cooperatively define a second sealing structure to regulate a flow of a lubricant between inside and outside of the bearing.

3. The parallel link mechanism as claimed in claim 2 , wherein the second sealing structure is defined in the form of a gap between an outer peripheral face of a part of the spacer member and an inner peripheral face of a part of the annular inner face forming portion.

4. The parallel link mechanism as claimed in claim 3 , wherein the annular inner face forming portion has a portion formed as an outer ring fit portion having an inner diameter equal to an outer diameter of the outer ring of the bearing, and the outer ring is fitted on the outer ring fit portion.

5. The parallel link mechanism as claimed in claim 3 , wherein the part of the annular inner face forming portion is formed as a stepped portion having an inner diameter smaller than that of a portion of the annular inner face forming portion that is fitted to the outer periphery of the outer ring of the bearing, and having a stepped surface configured to abut against an end face of the outer ring to axially position the outer ring.

6. The parallel link mechanism as claimed in claim 2 , wherein the inner ring fixation element is a nut threadedly engaged on a threaded portion formed in the shaft portion.

7. A parallel link mechanism comprising:

a proximal end side link hub;

a distal end side link hub; and

three or more link mechanisms that connect the distal end side link hub to the proximal end side link hub in a position-changeable fashion,

each of the link mechanisms having a trinodal structure with four revolute pairs, and including a proximal side end link member, one end of the proximal side end link member being pivotably connected to the proximal end side link hub; a distal side end link member, one end of the distal side end link member being pivotably connected to the distal end side link hub; and an intermediate link member which is pivotably connected to the other ends of the proximal side end link member and the distal side end link member, and

each of the link mechanisms having such a shape that a geometric model of the link mechanism represented by lines shows symmetry between a proximal end side portion thereof and a distal end side portion thereof with respect to a center portion of the intermediate link member,

wherein each revolute pair of each of the link mechanisms includes one pair of pair constituent members connected to each other via a bearing,

wherein one of the pair constituent members is formed with a shaft portion fitted to an inner periphery of an inner ring of the bearing, and the other of the pair constituent members is formed with an annular inner face forming portion fitted to an outer periphery of an outer ring of the bearing, the shaft portion and the annular inner face forming portion cooperatively define a first sealing structure to regulate a flow of a lubricant between inside and outside of the bearing, and

wherein the first sealing structure includes a labyrinth structure.