Apparatus for controlling relative movement of an optical head to an optical disk with velocity detection

In a velocity control system for controlling velocity of relative movement of an optical head to an optical disk, said control system provides a traverse signal having a frequency corresponding to said velocity of relative movement of the optical head to the optical disk and velocity detecting means, the improvement comprising:

• means for providing increased accuracy upon detection of reduced relative velocity, including in said velocity detecting means:
• counting means for counting during cycles of said traverse signal a reference clock signal having a frequency f, and memory means receiving as an input the count of said counting means, said memory means storing data inversely proportional to said input count and providing said stored data as a digital signal proportional to said velocity of relative movement,
• upper limit detecting means for determining when an upper limit is reached for the count of said counting means, said upper limit representing a low velocity limit,
• first means operable in response to detection of said upper limit by said upper limit detecting means for switching said reference clock pulse signal to have a reduced frequency f/N, thereby increasing the value of the inverse data output from said memory, and
• second means operable in response to detection of said upper limit by said upper limit detecting means to provide a multiplier means for mutliplying the output of said memory means by 1/N to provide said digital signal, thereby providing an N-fold increase in accuracy of the digital signal proportional to said velocity of relative movement for velocities below said low velocity limit.

In a velocity control system for controlling velocity of relative movement of an optical head to an optical disk, the improvement comprising:

• means for providing increased accuracy upon detection of reduced relative velocity, including:
• inverse function means for eliminating a low pass filter from a frequency to voltage converter,
• wherein said control system provides a traverse signal having a pulse width corresponding to radial travel time between tracks of the disk, and
• said inverse function means comprises velocity detecting means,
• said velocity detecting means including first limit detecting means for determining when a lower limit is reached for a shortened pulse width of said traverse signal occurring during times of fast velocity of movement and, in response thereto, obtaining counts of a reference clock pulse signal during said shortened pulse width, and access means for obtaining from a memory a value inversely proportional to the obtained counts during the pulse width and for outputting the obtained value as an output signal corresponding to said inverse value as a velocity signal;
• said velocity detecting means including second limit detecting means for determining when an upper limit is reached for a lengthened pulse width of said traverse signal occurring during times of reduced velocity of movement and, in response thereto dividing the reference clock frequency by a value N, obtaining counts of the divided frequency reference clock pulse signal during the lengthened pulse width, said access means operable for obtaining from the memory a value inversely proportional to the reduced counts of said reduced clock frequency, for dividing the value obtained from the memory by N to increase accuracy by a factor of N during the lengthened pulse width, and for outputting the obtained value as an output signal corresponding to said reduced velocity signal.

In a velocity control system for controlling velocity of relative movement of an optical head to an optical disk, the improvement comprising:

• means for providing increased accuracy upon detection of reduced relative velocity, including:
• inverse function means for eliminating a low pass filter from a frequency to voltage converter,
• wherein said control system provides a traverse signal having a frequency corresponding to said velocity of relative movement of the optical head to the optical disk, and
• said inverse function means comprises velocity detecting means including:
• counting means for counting during cycles of said traverse signal a reference clock signal having a frequency f, and memory means receiving as an input the count of said counting means, said memory means storing data inversely proportional to said input count and providing said stored data as a digital signal proportional to said velocity of relative movement,
• said velocity detecting means further including:
• upper limit detecting means for determining when an upper limit is reached for the count of said counting means, said upper limit representing a low velocity limit,
• first means operable in response to detection of said upper limit by said upper limit detecting means for switching said reference clock pulse signal to have a reduced frequency f/N, thereby increasing the value of the inverse data output from said memory, and
• second means operable in response to detection of said upper limit by said upper limit detecting means to provide a multiplier means for multiplying the output of said memory means by 1/N to provide said digital signal, thereby providing an N-fold increase in accuracy of the digital signal proportional to said velocity of relative movement for velocities below said low velocity limit.