Devices and methods for determining a critical rotation speed of an optical data carrier, monitoring a condition of an optical data carrier, and generating a reference signal

A method of determining a critical rotation speed of an optical data carrier at which a critical deflection of said optical data carrier may occur, said method comprising the steps of:

• rotating said optical data carrier according to a sweep covering a predetermined range of rotation speeds,
• generating a measurement signal indicative of a distance between a surface of said optical data carrier and a reference position, and
• determining said critical rotation speed of said optical data carrier by processing said measurement signal corresponding to said sweep on the basis of at least one characteristic of said measurement signal.

A device for generating a reference signal to be used for determining a critical rotation speed of an optical data carrier, said device comprising

• a reference drive unit for rotating a reference disc, said reference drive unit being adapted for rotating said reference disc according to a sweep covering a predetermined range of rotation speeds,
• a reference measurement unit for generating said reference signal indicative of a distance between a surface of said reference disc and a reference position, said reference signal corresponding to said sweep, and
• a surface unit for measuring the shape of said surface of said reference disc.

A method of generating a reference signal to be used for determining a critical rotation speed of an optical data carrier, said method comprising the steps of

• rotating a reference disc,
• generating said reference signal indicative of a distance between a surface of said reference disc and a reference position, said reference signal corresponding to a sweep covering a predetermined range of rotation speeds, and
• measuring the shape of said surface of said reference disc.