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A drive shaft assembly for a downhole motor includes a drive shaft formed with convexly spherical bearing surfaces on each end, and end housings with concavely spherical bearing surfaces for mating contact with the spherical bearing surfaces of the drive shaft, thereby facilitating omni-directional articulation between the drive shaft and the end housings while transferring axial thrust loads between the drive shaft and end housings across the interface of the mating spherical bearing surfaces. Torque is transferred between the drive shaft and end housings through two or alternatively four swivelling drive keys mounted to each end of the drive shaft and engageable with complementary drive key slots in the end housings. Full and constant torque-transferring contact is thus provided between the swivelling drive keys and the end housings irrespective of any angular offset between the drive shaft and the end housings, resulting from omni-directional articulation of the drive shaft relative to the end housing. The omni-directional center of rotation at each end of the drive shaft coincides with the geometric centerpoint of the corresponding convexly spherical bearing surface, which corresponds to the intersection of the drive shaft's rotational axis, the end housing's rotational axis, and the drive key swivel axis.

An apparatus, which includes a light source, a polarizing plate for converting the light beam to linearly polarized light, a half mirror for dividing the light beam into signal light and reference light and superimposing the signal light and the reference light on each other to produce interference light, a wavelength plate for converting the reference light to circularly polarized light, a frequency shifter for shifting a frequency of the reference light, a reference mirror which is moved by a piezoelectric element, a polarization beam splitter for extracting an S-polarized light component and a P-polarized light component from the interference light, CCDs for detecting the respective polarized light components and outputting detection signals, and portion for calculating a signal intensity of the interference light and a phase thereof based on the detection signals. An image of an object to be measured is formed based on a result obtained by calculation.

A turntable includes a rotatable member rotatable together with a display portion about a predetermined axis line, a fixed member disposed on one side of the rotatable member in a direction of the axis line, a first friction plate whose rotation about the axis line is restricted by the rotatable member (and movable relative to the rotatable member in a direction of the axis line), and a second friction plate whose rotation about the axis line is restricted by the fixed member (and movable relative to the fixed member in a direction of the axis line). The first friction plate and the second friction plate are disposed between the fixed member and the rotatable member in a direction of the axis line. At least, a sliding contact portion between the fixed member and the first friction plate, a sliding contact portion between the first friction plate and the second friction plate, and a sliding contact portion between the second friction plate and the rotatable member are provided.