Patent ID: 7893582

Claim:
A hollow motor drive device, comprising: a screw shaft provided with a spiral screw groove formed in an outer peripheral surface thereof; a nut member provided with a nut groove formed in an inner peripheral surface thereof so as to be screw-engaged with the screw groove; a hollow drive shaft having an inner peripheral side on which the nut member is fixed and an outer peripheral side on which a permanent magnet, as a field magnetic flux generating source, is disposed; and a housing provided with a bearing portion rotatably supporting the hollow drive shaft and a coil portion as a magnetic field generating source, wherein, in the hollow drive shaft, the nut member and the permanent magnet are disposed so as not to be overlapped with each other in a direction perpendicular to the axial direction of the hollow drive shaft, and in the housing, the bearing portion is disposed to a position corresponding to the nut member, and the coil portion is disposed to a position corresponding to the permanent magnet, and wherein the permanent magnet is provided for the hollow drive shaft through a position adjusting mechanism so as to adjust a distance between the permanent magnet and the coil portion, the position adjusting mechanism comprising a magnet holding member disposed so as to be connected to the permanent magnet, a spannring interposed between the magnet holding member and the hollow drive shaft, in which movement of one end side toward one end side axial direction is restricted by abutment of the one end against an engaging wall formed to the hollow drive shaft, a spacer sleeve disposed on another end side of the spannring to be movable in an axial direction of the hollow drive shaft, and a thrust nut pushing the spannring in the one end side axial direction through the spacer sleeve by screw-engagement with a screw groove formed in a surface of the hollow drive shaft.