1. Field of the Invention
This invention relates to a disc table employed in a disc recording/reproducing apparatus for a recording disc, such as an optical disc or a magneto-optical disc, on which information signals are to be recorded or prerecorded. More particularly, the present invention relates to such disc table having a centering member enabling the recording medium to be loaded and centered with respect to the disc table. The present invention also relates to a method for producing such disc table.
2. Description of the Related Art
Recently, recording discs, such as optical discs or magneto-optical discs, and a recording/reproducing apparatus employing such recording discs as a recording medium, have been proposed.
In the above-described recording/reproducing apparatus, when recording information signals on the recording disc or reproducing information signals recorded on the recording disc, the disc is rotated with a pickup unit which acts as a recording and/or reproducing means for the information signals, facing a signal recording surface of the disc. To this end, there is provided in the disc recording/reproducing apparatus a disc rotating and driving mechanism having a disc table on which the recording disc is loaded and which is adapted to be rotated in unison with the disc. Examples of such types of disc tables are disclosed in U.S. Pat. No. 4,068,851 to Yamamura and U.S. Pat. No. 4,340,955 to Elliott et al.
The disc table constituting the above-described disc rotating and driving mechanism comprises a table section integrated with a driving shaft of a rotating driving motor which functions as a rotating and driving means, and a fitting member mounted at the middle of the table section which engages in a center aperture of the recording disc set on the table section.
The disc table includes a thrusting and supporting mechanism for thrusting and supporting the recording disc set on the table section in a predetermined position. The thrusting and supporting mechanism comprises a chucking plate mounted facing the table section and adapted to clamp the rim of the center aperture of the recording disc set on the table section in position on the table section.
The fitting member is substantially frusto-conical, and tapered towards its upper or distal end.
The fitting member is supported for movement along the axis of the driving shaft, while being resiliently biased by a biasing member, such as a spring, towards its upper end.
With the above-described disc table, in which the outer periphery of the fitting member is tapered and upwardly biased when the recording disc is set on the table section, with the rim of the center aperture thereof in sliding contact with the outer periphery of the fitting member, the rim of the center aperture engages the outer periphery of the fitting member to effect a centering of the recording disc with respect to the driving shaft.
When the driving motor is driven to rotate the driving shaft, the recording disc is rotated in unison with the disc table.
Meanwhile, the above-described disc table in which the fitting member for centering the recording disc with respect to the disc table, is supported for movement relative to the table section, is complex in construction and difficult to assemble and manufacture. Besides, with this disc table, since it is necessary to provide a spring between the fitting member and the table section, it is difficult to achieve reduction in height of the table.
To overcome this drawback, a disc table has been proposed in which the fitting member is fixedly provided with respect to the table section to achieve a simplified construction and a reduction in the height of the apparatus. However, it is necessary with this disc table design that the fitting member be smaller in size with respect to the center aperture in order to allow for the dimensional error of the outer diameter of the fitting member and the dimensional error of the inside diameter of the center aperture. Consequently, with such disc table, a very small clearance tends to occur between the outer periphery of the fitting member and the inner rim of the center aperture when the recording disc is set on the table section.
If such clearance occurs between the fitting member and the center aperture, not only can the centering of the recording disc with respect to the driving shaft not be achieved, but also the recording disc tends to shift relative to the table section in response to external vibrations or shock.
Further, with the above-described recording/reproducing apparatus, if the offset of the recording disc with respect to the driving shaft of the disc rotating and driving mechanism is sufficiently large, the light beam from the pickup unit for writing and/or reading information signals on or from the recording disc cannot follow the recording track of the recording disc and renders it impossible to record and/or reproduce the information signals. Additionally, with such disc recording/reproducing apparatus, if the recording disc shifts with respect to the table section in the course of recording and/or reproduction of the information signals, the light beam undergoes track jump to interrupt recording/reproduction process.