Apparatus and method for driving a motor

A method for generating waveform data, which is the base of a pulse modulated signal used in subjecting a multiphase DC motor to the pulse modulated drive, the method comprising:

• rotating the multiphase DC motor at a predetermined rotational speed;
• sampling over a predetermined period a back electro-motive force induced at one end of at least one phase coil of the multiphase DC motor, with one end of each phase coil being set in a high impedance state;
• and
• storing the sampled back electro-motive force as waveform data.

A motor drive circuit of a multiphase DC motor comprising:

• a plurality of switching circuits, each of which is provided for each coil of the multiphase DC motor so as to apply a high-level or low-level voltage to one end of a corresponding coil;
• a back electro-motive force detecting circuit that compares a back electro-motive force induced in at least one coil of the multiphase DC motor with a midpoint voltage of the coils to detect a zero-cross point, and that outputs a back electro-motive force detecting signal at a predetermined level;
• a pulse signal generating circuit that receives the back electro-motive force detecting signal and that generates a pulse signal in synchronization with the back electro-motive force detecting signal, the frequency of the pulse signal being obtained by multiplying the frequency of the back electro-motive force detecting signal by n, where n indicates an integer of 2 or greater;
• a waveform data generating circuit that receives the pulse signal from the pulse signal generating circuit and that outputs predetermined waveform data in accordance with the pulse signal;
• a pulse modulated signal generating circuit that generates a pulse modulated signal by using the waveform data from the waveform data generating circuit;
• a switching control circuit that receives the back electro-motive force detecting signal from the back electro-motive force detecting circuit and the pulse modulated signal from the pulse modulated signal generating circuit and that controls a sequence of on/off states of the plurality of switching circuits based on the back electro-motive force detecting signal, and that subjects at least one of a high-side switch and a low-side switch included in each of the plurality of the switching circuits to switching control based on the pulse modulated signal;
• and
• a sampling circuit that, while running the multiphase DC motor at a predetermined rotational speed, samples over a predetermined period a back electro-motive force induced at one end of at least one phase coil, with one end of each phase coil of the multiphase DC motor being set in a high impedance state, wherein the waveform data generating circuit records as waveform data the back electro-motive force beforehand sampled by the sampling circuit.

A motor drive circuit of a multiphase DC motor comprising:

• a plurality of switching circuits, each of which is provided for each coil of the multiphase DC motor so as to apply a high-level or low-level voltage to one end of a corresponding coil;
• a back electro-motive force detecting circuit that compares a back electro-motive force induced in at least one coil of the multiphase DC motor with a midpoint voltage of the coils to detect a zero-cross point, and that outputs a back electro-motive force detecting signal at a predetermined level;
• a pulse signal generating circuit that receives the back electro-motive force detecting signal and that generates a pulse signal in synchronization with the back electro-motive force detecting signal, the frequency of the pulse signal being obtained by multiplying the frequency of the back electro-motive force detecting signal by n, where n indicates an integer of 2 or greater;
• a waveform data generating circuit that receives the pulse signal from the pulse signal generating circuit and that outputs predetermined waveform data in accordance with the pulse signal;
• a pulse modulated signal generating circuit that generates a pulse modulated signal by using the waveform data from the waveform data generating circuit;
• and
• a switching control circuit that receives the back electro-motive force detecting signal from the back electro-motive force detecting circuit and the pulse modulated signal from the pulse modulated signal generating circuit and that controls a sequence of on/off states of the plurality of switching circuits based on the back electro-motive force detecting signal, and that subjects at least one of a high-side switch and a low-side switch included in each of the plurality of the switching circuits to switching control based on the pulse modulated signal, wherein the waveform data generating circuit includes a memory that records the waveform data obtained by sampling over a predetermined period a back electro-motive force induced at one end of at least one phase coil of the multiphase DC motor, while rotating the motor at a predetermined rotational speed and setting one end of each phase coil of the motor in a high impedance state.

A method for subjecting a multiphase DC motor to switch driving by using a pulse modulated signal, the method comprising:

• rotating the multiphase DC motor at a predetermined rotational speed;
• reading waveform data stored in a memory such that a pulse modulated signal, the pulse width of which varies in accordance with the waveform data, is generated accordingly;
• subjecting the multiphase DC motor to the switch driving by using the pulse modulated signal;
• measuring a physical quantity indicating a rotational state of the multiphase DC motor;
• and
• updating the waveform data stored in the memory such that the measured physical quantity is brought close to a target value.

A drive circuit of a multiphase DC motor comprising:

• a plurality of switching circuits, each of which is provided for each coil of the multiphase DC motor so as to apply a high-level or low-level voltage to one end of a corresponding coil;
• a back electro-motive force detecting circuit that compares a back electro-motive force induced in at least one coil of the multiphase DC motor with a midpoint voltage of the coils to detect a zero-cross point, and that outputs a back electro-motive force detecting signal at a predetermined level;
• a pulse signal generating circuit that receives the back electro-motive force detecting signal and that generates a pulse signal in synchronization with the back electro-motive force detecting signal, the frequency of the pulse signal being obtained by multiplying the frequency of the back electro-motive force detecting signal by n, where n indicates an integer of 2 or greater;
• a waveform data generating circuit that includes a waveform data memory for storing waveform data, and that outputs the waveform data in accordance with the pulse signal from the pulse signal generating circuits;
• a pulse modulated signal generating circuit that generates a pulse modulated signal by using the waveform data from the waveform data generating circuit;
• a switching control circuit that receives the back electro-motive force detecting signal from the back electro-motive force detecting circuit and the pulse modulated signal from the pulse modulated signal generating circuit and that controls a sequence of on/off states of the plurality of switching circuits based on the back electro-motive force detecting signal, and that subjects at least one of a high-side switch and a low-side switch included in each of the plurality of the switching circuits to switching control based on the pulse modulated signal;
• a sensor by which a physical quantity indicating a rotational state of the multiphase DC motor is measured;
• and
• an encoder that updates the waveform data stored in the memory such that the physical quantity measured by the sensor is brought close to a target value.

A motor drive circuit of a multiphase DC motor comprising:

• a plurality of switching circuits, each of which is provided for each coil of the multiphase DC motor so as to apply a high-level or low-level voltage to one end of a corresponding coil;
• a back electro-motive force detecting circuit that compares a back electro-motive force induced in at least one coil of the multiphase DC motor with a midpoint voltage of the coils to detect a zero-cross point, and that outputs a back electro-motive force detecting signal at a predetermined level;
• a pulse signal generating circuit that receives the back electro-motive force detecting signal and that generates a pulse signal in synchronization with the back electro-motive force detecting signal, the frequency of the pulse signal being obtained by multiplying the frequency of the back electro-motive force detecting signal by n, where n indicates an integer of 2 or greater;
• a waveform data generating circuit that includes a waveform data memory for storing waveform data, and that outputs the waveform data in accordance with the pulse signal from the pulse signal generating circuits;
• a pulse modulated signal generating circuit that generates a pulse modulated signal by using the waveform data from the waveform data generating circuit;
• a switching control circuit that receives the back electro-motive force detecting signal from the back electro-motive force detecting circuit and the pulse modulated signal from the pulse modulated signal generating circuit and that controls a sequence of on/off states of the plurality of switching circuits based on the back electro-motive force detecting signal, and that subjects at least one of a high-side switch and a low-side switch included in each of the plurality of the switching circuits to switching control based on the pulse modulated signal;
• and
• an interface circuit that receives waveform data from an outside processor to write the data into the waveform data memory.