Patent ID: 7906928

Claim:
A lock detection device for checking whether a feed motor is in a driven state or in a non-driven state, the feed motor including an A-phase coil driven by an A-phase motor driver and a B-phase coil driven by a B-phase motor driver, the lock detection device comprising: an A-phase magnetic polarity change detector arranged to generate an A-phase magnetic polarity change detection signal according to a change in A-phase magnetic polarity of the feed motor; a B-phase magnetic polarity change detector arranged to generate a B-phase magnetic polarity change detection signal according to a change in B-phase magnetic polarity of the feed motor; an A-phase back electromotive voltage detector arranged to detect an A-phase back electromotive voltage appearing in the A-phase coil; a B-phase back electromotive voltage detector arranged to detect a B-phase back electromotive voltage appearing in the B-phase coil; a checker arranged to recognize the feed motor to be in the driven state when at least one of the A- and B-phase back electromotive voltages is higher than a predetermined level and recognize the feed motor to be in the non-driven state when both the A- and B-phase back electromotive voltages are lower than the predetermined level; an A-phase driver control signal generator arranged to generate and feed to the A-phase motor driver an A-phase driver control signal based on the A-phase magnetic polarity change detection signal such that both ends of the A-phase coil are turned into a high-impedance state near a change in A-phase magnetic polarity; and a B-phase driver control signal generator arranged to generate and feed to the B-phase motor driver a B-phase driver control signal based on the B-phase magnetic polarity change detection signal such that both ends of the B-phase coil are turned into a high-impedance state near a change in B-phase magnetic polarity, wherein: the A-phase driver control signal generator generates and feeds to the A-phase motor driver the A-phase driver control signal such that the A-phase coil stops being driven when both ends of the B-phase coil are in a high-impedance state, the B-phase driver control signal generator generates and feeds to the B-phase motor driver the B-phase driver control signal such that the B-phase coil stops being driven when both ends of the A-phase coil are in a high-impedance state, the A-phase back electromotive voltage detector detects the A-phase back electromotive voltage when both ends of the A-phase coil are in a high-impedance state, and the B-phase back electromotive voltage detector detects the B-phase back electromotive voltage when both ends of the B-phase coil are in a high-impedance state.