Brushless DC motor and image pickup apparatus
A brushless DC motor configured to drive a driven member includes a rotor having a magnet, a stator having a coil configured to provide a rotational force to the magnet, a position detector configured to output a first signal that is periodic, in accordance with a rotating position of the rotor, a signal generator configured to generate a second signal by adding a lead angle to a phase of the first signal output from the position detector, an excitation switch configured to select an excitation to the coil in accordance with the second signal, and a phase change part configured to change the lead angle in accordance with at least one of a position and a moving direction of the driven member.
1. A brushless DC motor configured to drive a driven member, said brushless DC motor comprising:
a rotor having a magnet;
a stator having a coil configured to provide a rotational force to the magnet;
a position detector configured to output a first signal that is periodic, in accordance with a rotating position of the rotor;
a signal generator configured to generate a second signal by adding a lead angle to a phase of the first signal output from the position detector;
an excitation switch configured to select an excitation to the coil in accordance with the second signal; and
a phase change part configured to change the lead angle in accordance with at least one of a position and a moving direction of the driven member.
2. The brushless DC motor according to claim 1 , wherein the position detector includes a first position detector configured to generate the first signal that has a sine wave shape, and a second detector configured to generate the first signal having a cosine wave shape, and
wherein the signal generator includes:
a first inverting amplifier connected to the first position detector and configured to amplify an output of the first position detector by −A times;
a second inverting amplifier connected to an output of the first inverting amplifier and configured to amplify the output of the first inverting amplifier by −1 times;
a third inverting amplifier connected to the second position detector and configured to amplify an output of the second position detector by −A times;
a fourth inverting amplifier connected to an output of the third inverting amplifier and configured to amplify the output of the third inverting amplifier by −1 times;
a fifth inverting amplifier configured to add an output of the second inverting amplifier amplified by cos α times to an output of the fourth inverting amplifier amplified by sin α times; and
a sixth inverting amplifier configured to add the output of the first inverting amplifier amplified by sin α times to the output of the fourth inverting amplifier amplified by cos α times, a being the lead angle.
3. The brushless DC motor according to claim 1 , wherein the phase change part includes:
a memory configured to store a relationship between at least one of the position and the moving direction of the driven member and the load used to drive the driven member, and a relationship between the load, a target speed for driving the driven member, and a plurality of lead angles; and
a selector configured to select one of the plurality of lead angles which is closest to the target speed to the load corresponding to the at least one.
4. A brushless DC motor configured to drive a driven member, said brushless DC motor comprising:
a rotor having a magnet;
a stator having a coil configured to provide a rotational force to the magnet;
a position detector configured to output a first signal that is periodic, in accordance with a rotating position of the rotor;
a signal generator configured to generate a second signal by adding a lead angle to a phase of the first signal output from the position detector;
an excitation switch configured to select an excitation to the coil in accordance with the second signal; and
a phase change part configured to change the lead angle in accordance with a load used to drive the driven member.
5. An image pickup apparatus comprising:
a lens as a driven member; and
a brushless DC motor according to claim 1 configured to drive the driven member.