Patent ID: 9019805
Filing Date: 2015-04-28
Classification: G11B

Abstract:
1. A drive device comprising: a spindle device which rotates a multilayer optical recording medium having: a guide layer group that is provided on a substrate and has guide layers having positional information in a radial direction recorded therein; and recording layers that are provided on the substrate and configured to record information therein; an optical device which comprises: an objective lens that faces the multilayer optical recording medium rotated by the spindle device; driving means for driving the objective lens to an arbitrary position in the radial direction; a supply source that emits laser beams having different wavelengths which are supplied to the guide layers and the recording layers, respectively; a light receiving element that receives the laser beams reflected by the guide layers and the recording layers; and a lens device that guides the laser beams to the objective lens and the light receiving element and is configured to perform focusing and tracking of the laser beams; and a control device which is configured to reproduce information recorded in the guide layers and the recording layers by using reflected lights of the laser beams applied to the guide layers and the recording layers when the recording layers are irradiated with the laser beams by the optical device, reproduces the positional information stored in the guide layers, and derives positional information of the recording layers associated with the positional information recorded in the guide layers at the positions of the recording layers in the radial direction and control information of the optical device that maximizes reflected light volumes of the laser beams of the guide layers and the recording layers at the positions; wherein the control device derives a degree of warpage of the multilayer optical recording medium from a difference between the derived pieces of control information at the positions in the radial direction; wherein the control device comprises a memory unit which stores a threshold value of the degree of warpage for reproduction and recording in the multilayer optical recording medium; and the control unit compares the derived degree of warpage with the threshold value, and determines that the degree of warpage of the multilayer optical recording medium is a degree of warpage that allows reproduction and recording in the multilayer optical recording medium when the degree of warpage falls within a range of the threshold value.