Ball screw mechanism and linear moving device

A ball screw mechanism comprising:

• a screw shaft that includes a spiral groove and extends linearly;
• a moving body that includes a housing provided so as to surround a periphery of the screw shaft;
• and
• a power transmission mechanism that transmits a thrust of the screw shaft to the housing of the moving body to move the moving body in an axial direction of the screw shaft, wherein
• the power transmission mechanism includes a plurality of ball bearings, a plurality of spheres respectively corresponding to the ball bearings, and a plurality of fixing screws, each of the fixing screws contacting a first side of the respective ball bearings that does not face the screw shaft,
• the housing has a plurality of hole portions into which the plurality of ball bearings can be inserted,
• the ball bearings each include, with a second side surface facing the screw shaft, an outer ring attached and fixed to the housing of the moving body at regular intervals along the spiral groove of the screw shaft, and an inner ring located inside the outer ring and with a concave spherical contact surface formed on the second side surface facing the screw shaft, the concave spherical contact surface being in contact with the spheres, and balls in contact with the outer ring and the inner ring,
• each of the inner rings is rotatably disposed about a rotation axis in a direction orthogonal to a rotation axis of the screw shaft, and the spheres are arranged, each in contact with the concave spherical contact surface, at regular intervals adjacent to each other in the spiral groove of the screw shaft,
• a bottom of the spiral groove is provided with a groove to avoid contact with the spheres,
• the balls are sandwiched along the radial direction of the outer ring and the inner ring by being installed in depressions formed opposite each other on an inner peripheral surface of the outer ring and an outer peripheral surface of the inner ring,
• the outer ring is sandwiched along the rotation axis direction of the inner ring by one of the fixing screws and a bottom of the respective hole portions, and
• an inner diameter of a side end of the inner ring where the concave spherical contact surface is formed is larger than the diameter of the spheres.