Disc record/reproduce apparatus with brushless motor having rotational speed controlled by a disc

Claim 1

A disc record/reproduce apparatus for recording/reproducing data on/from a sector of a record disc, said disc record/reproduce apparatus having a brushless dc motor for rotating said record disc, said brushless dc motor having a plurality of windings, comprising: (a) drive means responsive to phase signals and an electric power for producing drive signals supplied to the windings of said brushless dc motor respectively to rotate said record disc; (b) back-electromotive force signal producing means responsive to back-electromotive forces of at least two of said windings of said brushless dc motor for producing back-electromotive force signals; (c) read/write head means for reading data including a second position signal recorded at every sector from said record disc, the number of said windings and said sector having a given relation therebetween; (d) microprocessor means including: (I) a/d-converting means responsive to said back-electromotive force signals for converting said back-electromotive force signals into digital back-electromotive force signals; (II) first position signal detecting means responsive to said digital back-electromotive force signals for producing a first position signal of said brushless dc motor; (III) start-up clock signal producing means for producing a start-up clock signal; (IV) start-up detection means responsive to one of said digital back-electromotive force signals for comparing one of said digital back-electromotive force signals with a given intensity value to produce a start-up switching signal; (V) first switching means responsive to said start-up switching signal for selecting between said start-up clock signal and a third position signal; (VI) phase signal producing means responsive to an output of said first switching means for producing said phase signals; (VII) second position signal detecting means responsive to said data read from said record disc for detecting said second position signal; (VIII) second switching means responsive to a second switching signal for selecting between said first position signal and said second position signal to output as said third position signal; (IX) speed signal producing means responsive to said third position signal for producing a speed signal in accordance with an interval of succeeding pulses of said third position signal; (X) comparing means for comparing said speed signal with a second given value to produce a lock-up signal; (XI) control means for recording/reproducing said data in response to a record command signal including said data and to a reproduce command signal from an external computer; and for causing said a/d-converting means, said first position signal detection means, and said start-up detection means to be disabled in response to said lock-up signal and then producing said second switching signal to select said second position signal as said third position signal in order to prevent overload in processing speed of said microprocessor means; and (e) speed control means responsive to said speed signal for controlling a speed of said brushless dc motor by controlling said electric power.