Detection of instantaneous position of the rotor of a brushless DC motor driven in a tripolar mode

A method for sensing position of a rotor of a multi-phase brushless motor using a zero-cross detecting circuit for respective phase windings of the motor driven in a multi-polar mode by respective driving stages, each zero-cross detecting circuit comprising a differential amplifier, the method comprising the steps of:

• interrupting driving of at least one of the phase windings of the motor by placing in a high impedance state an output of a respective driving stage using a first logic signal;
• closing for a predetermined time beginning with a switching instant of the first logic signal a short-circuiting switch for inputs of the differential amplifier of the at least one zero-crossing detecting circuit using a second logic signal;
• enabling an asserting logic gate of a zero-cross event detected by the zero-cross detecting circuit starting from an instant of re-opening of the short-circuiting switch using a third logic signal;
• and
• resetting the first logic signal and the third logic signal a period of time after the interrupting.

A method of sensing a position of a rotor of a multi-phase brushless motor using at least one zero-cross detecting circuit for a respective phase winding of the motor driven in a multi-polar mode using at least one driving stage, the at least one zero-cross detecting circuit comprising a differential amplifier, the method comprising the steps of:

• interrupting driving of at least one of the phase windings of the motor by placing in a high impedance state an output of a respective driving stage using a first logic signal, the interrupting being for a time duration dynamically regulated as a function of a correct or incorrect forecast of a next zero-cross instant;
• closing for a predetermined time beginning with a switching instant of the first logic signal a short-circuiting switch for inputs of the differential amplifier of the at least one zero-crossing detecting circuit using a second logic signal;
• enabling an asserting logic gate of a zero-cross event detected by the zero-cross detecting circuit starting from an instant of re-opening of the short-circuiting switch using a third logic signal;
• and
• resetting the first logic signal and the third logic signal a period of time after the interrupting.

A system for driving a multi-phase brushless motor of a type comprising a plurality of phase windings and a rotor, the system comprising:

• a plurality of power driver stages, each for driving respective phase windings of the motor;
• storage means for storing digitized samples of driving waveforms for the phase windings;
• a plurality of digital/analog converters for converting digital values of samples into an analog driving signal;
• synchronizing means for synchronizing conversions of samples read from said storage means with a signal representative of a position of the rotor of the motor;
• logic means for reconstructing a plurality of mutually out-of-phase sequences of the driving waveforms from the samples;
• said synchronizing means further comprising a detecting circuit for sensing at least a zero-cross of at least a back-electromotive-force signal induced on a phase winding, said detecting circuit comprising
• a differential amplifier and a short-circuiting switch for short-circuiting inputs of said differential amplifier;
• first logic means for generating a first logic command for setting in a condition of high impedance at an output of a respective power driver stage for the phase winding,
• second logic means for generating a second logic command for closing for a constant and predetermined interval of time starting from the switching instant of the first logic command the short-circuit switch,
• a logic gate for generating a zero-cross assertion signal, and
• third logic means for generating a third logic command for enabling an output of the zero-cross assertion signal by said logic gate starting from an instant when the short-circuiting switch re-opens at the end of the predetermined interval of time,
• said first and third logic means resetting the first and third logic commands after a certain interval of time.

A method for sensing position of a rotor of a multi-phase brushless motor using at least one zero-cross detecting circuit for voltage induced on a respective phase winding of the motor driven in a multi-polar mode using at least one driving stage, the at least one zero-cross detecting circuit comprising a comparator, the method comprising the steps of:

• interrupting a driving current of at least one of the phase windings of the motor coupled to a respective zero-cross detecting circuit by placing in a high impedance state an output of a respective driving stage using a first logic signal;
• enabling an asserting logic gate of a zero-cross event detected by the zero-cross detecting circuit starting a certain time after interrupting the driving current using a third logic signal;
• and
• resetting the first logic signal and the third logic signal a period of time after the interrupting.

A method for sensing position of a rotor of a multi-phase brushless motor using a zero-cross detecting circuit for respective phase windings of the motor driven in a multi-polar mode by respective driving stages, the method comprising the steps of:

• interrupting driving of at least one of the phase windings of the motor by placing in a high impedance state an output of a respective driving stage using a first logic signal;
• enabling an asserting logic gate of a zero-cross event detected by the zero-cross detecting circuit starting a certain time after the interruption of the driving current using a third logic signal;
• and
• resetting the first logic signal and the third logic signal a period of time after the interrupting.

A method of sensing a position of a rotor of a multi-phase brushless motor using at least one zero-cross detecting circuit for a respective phase winding of the motor driven in a multi-polar mode using at least one driving stage, the method comprising the steps of:

• interrupting driving of at least one of the phase windings of the motor by placing in a high impedance state an output of a respective driving stage by means of a first logic signal, the interrupting being for a time duration dynamically regulated as a function of a correct or incorrect:
• forecast of a next zero-cross instant;
• enabling an asserting logic gate of a zero-cross event detected by the zero-cross detecting circuit starting a certain time after the interruption of the driving current by means of a third logic signal;
• and
• resetting the first logic signal and the third logic signal a period of time after the interrupting.

A system for driving a multi-phase brushless motor of,a type comprising a plurality of phase windings and a rotor, the system comprising:

• a plurality of power driver stages, each for driving respective phase windings of the motor;
• storage means for storing digitized samples of driving waveforms for the phase windings;
• a plurality of digital/analog converters for converting digital values of samples into an analog driving signal;
• synchronizing means for synchronizing conversions of samples read from said storage means with a signal representative of a position of the rotor of the motor;
• logic means for reconstructing a plurality of mutually out-of-phase sequences of the driving waveforms from the samples;
• said synchronizing means further comprising a detecting circuit for sensing at least a zero-cross of at least a back-electromotive-force signal induced on a phase winding, said detecting circuit comprising
• a comparator connected to the phase winding,
• first logic means for generating a first logic command for setting in a condition of high impedance at an output of a respective power driver stage for the phase winding,
• a logic gate connected to said comparator for generating a zero-cross assertion signal, and
• third logic means for generating a third logic command for enabling an output of the zero-cross assertion signal by said logic gate starting a certain time after the interruption of the driving current,
• said first and third logic means resetting the first and third logic commands after a certain interval of time.