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In a caster which supports a wheel by using via a link 3 a bracket 2 to be fitted to a wheelchair or the like, an end of the link 3 is connected with a rotation axis of the bracket 2 via a rubber member 8 which is twisted and deformed resulting from oscillating motion of the link 3, and the link 3 a

In a caster which supports a wheel by using via a link 3 a bracket 2 to be fitted to a wheelchair or the like, an end of the link 3 is connected with a rotation axis of the bracket 2 via a rubber member 8 which is twisted and deformed resulting from oscillating motion of the link 3, and the link 3 and the bracket 2 are connected by a hydraulic damper 20 which damps the oscillating motion of the link 3, whereby an oscillation or a shock can be absorbed.

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1. A caster suitable to be fitted to a wheelchair, comprising: a bracket; a link having one end pivotally connected to the bracket via a rubber bush that twists and deforms in response to an oscillating motion of the link; a wheel rotatably mounted to the other end of the link; and a hydraulic

1. A caster suitable to be fitted to a wheelchair, comprising: a bracket; a link having one end pivotally connected to the bracket via a rubber bush that twists and deforms in response to an oscillating motion of the link; a wheel rotatably mounted to the other end of the link; and a hydraulic damper connected between the link and the bracket to damp the oscillating motion of the link; wherein the hydraulic damper comprises a tube having one end connected to the bracket and an other end being open, an end member spirally engaging a screw section provided on an inner surface of the other end of the tube, a piston rod engaged slidably with the end member and having one end connected to the link, and a piston connected to an other end of the piston rod. 2. A caster according to claim 1, wherein the hydraulic damper is filled with a viscous hydraulic operating fluid as a hydraulic operating fluid and a pressure of the viscous hydraulic operating fluid supports a load applied to the bracket. 3. A caster according to claim 2, wherein the viscous hydraulic operating fluid is silicon oil. 4. A caster according to claim 2, wherein the piston partitions an inside of the damper tube into two oil rooms, the configuration of the piston being such that a space is formed between the damper tube and the piston that connects the two oil rooms. 5. A caster according to claim 4, wherein the piston includes a cylindrical section engaged with the piston rod and a discoid section with the space formed between the damper tube and the piston. 6. A caster according to claim 2, wherein a compression ratio of the viscous hydraulic operating fluid can be varied. 7. A caster suitable to be fitted to a wheelchair, comprising: a bracket; a link having one end pivotally connected to the bracket via a rubber bush that twists and deforms in response to an oscillating motion of the link; a wheel rotatably mounted to the other end of the link; and a hydraulic damper connected between the link and the bracket to damp the oscillating motion of the link; wherein the link can be adjusted in length to vary a distance between a center of the oscillation motion of the link and a center of the rotation of the wheel. 8. A caster according to claim 7, wherein the link comprises: a supporting cylinder; a movable shaft which is slidably inserted in the supporting cylinder; a plurality of positioning holes disposed along the length of the supporting cylinder and the movable shaft; and a positioning pin for adjusting a longitudinal position of the movable shaft by insertion in selected ones of the positioning holes. 9. A caster suitable to be fitted to a wheelchair, comprising: a bracket; a link having one end pivotally connected to the bracket via a rubber bush that twists and deforms in response to an oscillating motion of the link; a wheel rotatably mounted to the other end of the link; a hydraulic damper connected between the link and the bracket to damp the oscillating motion of the link; and two levers pivotally connected between the bracket and the link, one of the levers being equipped, at an end at which the levers are connected to each other, with a restraint mechanism having a claw section for locking relative positions of the two levers, so as to fix the wheel at a predetermined position. 10. A caster suitable to be fitted to a wheelchair, comprising: a bracket; a link having one end pivotally connected to the bracket via a rubber bush that twists and deforms in response to an oscillating motion of the link; a wheel rotatably mounted to the other end of the link; and a hydraulic damper connected between the link and the bracket to damp the oscillating motion of the link; wherein the link can be adjusted in length to maintain a height of the bracket above the center of rotation of the wheel when a load applied to the caster changes.