Abstract: The ball joint includes: a ball stud including: a shaft member; and a ball portion formed at one end of the shaft member; and a holder made of a synthetic resin and configured to accommodate the ball portion in a pivotable manner. The holder includes: an opening portion from which the shaft member protrudes; a first member including a first ball sliding contact surface having a concave spherical shape approximate to a spherical surface of the ball portion; and a second member including: a second ball sliding contact surface having a concave spherical shape approximate to the spherical surface of the ball portion; and the opening portion formed in a center of the second ball sliding contact surface. Further, the first member and the second member respectively include joining surfaces fixed to each other by welding, and respectively include fixation reference surfaces that are brought into abutment against each other.

Abstract: An optical disc apparatus includes a fixed portion having a light source portion and a movable portion that holds an objective lens and moves along a radial direction of an optical disc. The fixed portion includes the light source portion for selectively emitting short and long wavelength laser beams, and a collimator lens for collimating the laser beams. The objective lens includes a positive refractive lens and a diffractive lens structure formed on a surface of the refractive lens. The diffractive lens structure has wavelength dependence such that spherical aberration varies in the undercorrected direction as wavelength of incident light increases. The objective lens converges the short wavelength laser beam of a predetermined diffraction order onto an informatlon layer of a thin cover type optical disc, and converges the long wavelength laser beam of the identical diffraction order onto an information layer of a thick cover type optical disc.

Abstract: A detecting apparatus which detects an inclination of an objective lens relative to a reference surface is provided. The objective lens is part of an optical data recording and reproducing apparatus in which data is optically recorded on and reproduced from a recording medium which is placed parallel to the reference surface. The apparatus includes a transparent parallel plate which is opposite the objective lens, parallel to the reference surface, and made of a material that is substantially optically equivalent to a transparent material of the recording medium. The apparatus further includes a reflecting mechanism for reflecting coherent light which has passed through the objective lens and the transparent parallel plate back towards the transparent parallel plate and the objective lens, and a beam splitting mechanism for splitting the coherent light into a first beam and a second beam.

Abstract: The optical disk apparatus of this invention is provided with a memory for memorizing a track offset signal corresponding to an angle of a galvanic mirror, or a photodetector having two pairs of photodetecting regions to detect different tracking error signals to each other, or two galvanic mirrors which are adjusted so as to prevent the track offset signal.