Gear mechanism

A gear mechanism comprising:

• a central gear rotatably supported on a rotational shaft;
• at least three through-hole cavities provided in said central gear in radial direction thereof;
• first and second side gears which are rotatably supported on said rotational shaft and coaxially positioned on both sides of said central gear in an axial direction of said rotational shaft;
• at least three planetary bevel gears rotatably supported in said through-hole cavities, respectively, of said central gear;
• sun bevel gears which are respectively formed on inner side surfaces, which face said central gear, of said first and second side gears to be engaged with said planetary bevel gears;
• and
• a torque adjuster for adjusting torque between said first and second said side gears.

A lens barrel comprising:

• a central gear rotatably supported on a rotational shaft, said central gear being connected to a driven lens that is provided in said lens barrel so that the rotation of said central gear causes said driven lens to move in an optical axis direction thereof;
• a side gear which is rotatably supported on said rotational shaft and coaxially positioned on one side of said central gear in an axial direction of said rotational shaft;
• planetary bevel gears incorporated in said central gear and rotatably supported within side surfaces of said central gear;
• sun bevel gears which are respectively formed on inner side surfaces, which face said central gear, of said side gear to be engaged with said planetary bevel gears;
• and
• a torque adjuster for adjusting torque in a rotating direction of said side gear, so that when said side gear is rotated, the rotation of said side gear is transmitted to said driven lens through said central gear, whereas when an external force is applied to said driven lens to move said driven lens in an optical axis direction, the rotation of said side gear is restricted so as not to move said driven lens.