Method and apparatus for driving a brushless motor

Claim 3

A method as claimed in claim 1 wherein the step of detecting an harmonic component includes generating a simulated signal in response to the phase energising signals applied to the phases of the motor; providing from the motor an actual composite signal having an induced back emf component and a phase energising signal component; and obtaining the difference between the simulated and actual composite signals to produce a difference signal.

Claim 4

A method as claimed in claim 1 or 2 further comprising the step of filtering the difference signal to remove noise components therefrom.

Claim 6

A method as claimed in claim 4 wherein the step of sensing when the harmonic component crosses a reference level comprises comparing the harmonic component to the reference level, generating a rectangular waveform having a positive-going portion when the harmonic content exceeds the reference level and a negative-­going portion when the harmonic component falls below the reference level, and generating a clock pulse at each positive-going and negative-going portion of the rectangular waveform.

Claim 7

A method as claimed in claim 4 or 5 wherein the step of using the phase energising signals to energise the phases of the motor in predetermined sequence comprises switching a source of energising current to a respective phase in response to a corresponding decoded phase energising signal.

Claim 8

A method as claimed in claim 6 wherein the motor is a bipolar motor (10) and wherein the step of using the phase energising signals to energise the phases of the motor further includes conducting the energising current through another phase in response to a decoded phase energising signal, whereby energising current flows through two phases at each decoded count.

Claim 10

A method as claimed in claim 8 wherein the step of controlling comprises sensing a current flowing through energised phases of the motor, providing a command current level determined by the command signal, comparing the sensed current to the command current level, and adjusting the magnitude of the current flowing through the energised phases to minimise any difference between the sensed current and the command current level.

Claim 13

Apparatus for driving an n-phase, m-pole (n and m are integers) brushless motor (10) comprising: harmonic detecting means (12) for detecting an harmonic component of back emf induced in the phases of the motor; phase energising means (24) responsive to the harmonic component for generating phase energising signals to energise selected phases of the motor; and drive current means for supplying drive current to those phases energised by the phase energising signals.

Claim 14

Apparatus for driving an n-phase, m-pole (n and m are integers) brushless motor (10) comprising: harmonic detecting means (12) for detecting an harmonic component of back emf induced in the phases of the motor; phase energising means (24) responsive to the harmonic component for generating phase energising signals to energise selected phases of the motor; and drive current means for supplying drive current to those phases energised by the phase energising signals.

Claim 15

Apparatus as claimed in claim 12 wherein the harmonic detecting means comprise circuit means (12) connected in parallel with the n phases of the motor; and difference means (14) coupled to the n phases of the motor and to the circuit means for producing a difference signal representing the difference between a composite signal, supplied from the n phases and having an induced back emf component and a phase energising component, and a simulated signal supplied from the circuit means and having components produced by the parallel connection.

Claim 16

Apparatus as claimed in claim 13 wherein the circuit means comprise a resistive network (12).

Claim 17

Apparatus as claimed in claim 14 wherein the n phases are connected in a star array having a common terminal for supplying the composite signal; and the resistive network comprises at least one star array of resistors (121,122,123) having a common terminal for supplying the simulated signal.

Claim 18

Apparatus as claimed in any of claims 12 to 15 wherein n=3 and the or each star array comprises a Y-­configuration.

Claim 19

Apparatus as claimed in claim 13 wherein the difference means include low pass filter means (141,142) for removing from the difference signal noise caused by currents flowing in the phases.

Claim 20

Apparatus as claimed in any preceding claim wherein the drive current means include variable current means (241,243,245) coupled to the phases and means for adjusting the current if the motor rotates at a speed which differs from a command speed.

Claim 21

Apparatus as claimed in claim 18 wherein the means for adjusting the current comprise command signal means (112) for providing a current command signal representing a desired motor current, sensing means for sensing actual motor speed and for generating the current command signal as a function thereof, error means (28) for producing an error signal as a function of the difference between the current command signal and actual motor current, and means for using the error signal to adjust the current flowing in the phases.

Claim 22

Apparatus as claimed in claim 19 wherein the variable current means comprise n transistor switch means coupled to the n phases, respectively, and means for supplying the error signal as a bias signal to the n transistor switch means to control the current flowing therethrough.

Claim 23

Apparatus as claimed in any of claims 12 to 17 wherein the drive current means comprise a first set of n switch means (241,243,245) coupled between a source of motor power and the n phases, respectively, a second set of n transistor switch means (242,244,246) coupled to the n phases, respectively, and means for applying the phase energising signals to a respective one of the switch means in the first set and to a respective one of the transistor switch means in the second set, whereby current flows through the respective switch means in the first set, two of the phases, and the respective transistor switch means in the second set.

Claim 24

Apparatus as claimed in claim 21 wherein the drive current means further comprise error detecting means (28) for detecting an error between actual motor current and desired motor current, and means (281) for superimposing a bias signal onto the phase energising signals applied to the second set of transistor switch means as a function of the detected error to reduce the error.

Claim 25

Apparatus as claimed in any of claims 12 to 21 wherein the phase energising means comprise pulse generating means (18) for generating pulses at predetermined locations of the harmonic component, and sequencing means (22) responsive to the pulses for generating the phase energising signals in a selected sequence.

Claim 26

Apparatus as claimed in claim 21 wherein the sequencing means comprise counting means (20) for counting the pulses and decoding means (22) for decoding the count of the counting means to produce the sequence of phase energising signals.

Claim 27

Apparatus as claimed in claim 24 wherein the pulse generating means comprise first and second comparator means (162,171) exhibiting first and second different hysteresis characteristics, respectively, for generating first and second rectangular waveforms when the harmonic component crosses a reference level; and wherein the counting means include an input stage (201) whose state is determined by the polarity of one of the rectangular waveforms at a time determined by the other.

Claim 28

Apparatus as claimed in claim 25 wherein the input stage comprises flip-flop means (201) having a data input (D) for receiving the one rectangular waveform and a clock input; and further comprising edge detecting means (163) for receiving the other rectangular waveform to produce a clock pulse in response to a transition in the other rectangular waveform.

Claim 29

Apparatus as claimed in claim 24, 25 or 26 wherein the pulse generating means comprise zero cross detecting means (16) for generating the pulses at zero level crossing points of the harmonic component.

Claim 30

Apparatus as claimed in any of claims 12 to 27 wherein the harmonic component is the third harmonic of the back emf.

Claim 31

Apparatus as claimed in any of claims 24 to 28 wherein n = 3 and the decoding means include means for energising two of the three phases concurrently.

Claim 32

Apparatus as claimed in any of claims 12 to 29 further comprising start-up means (30) coupled to the phase energising means for controlling the phase energising signals generated to start up the rotation of the motor, the start-up means including means for supplying a clock signal at a relatively low frequency to the phase energising means for a first predetermined time period, means for increasing the frequency of the clock signal for a second predetermined time period, and means for terminating the clock signal supplied to the phase energising means at the completion of the second predetermined time period.

Claim 33

Apparatus as claimed in claim 30 wherein the start-up means further include means for controlling the drive current means to supply a drive current whose amplitude gradually increases over the first predetermined time period in a ramp-like manner from a relatively low reference level to a motor drive level.

Claim 34

Apparatus as claimed in claim 30 or 31 wherein the start-up means further include means for delaying the beginning of the second predetermined time period relative to the completion of the first predetermined time period.

Claim 37

Apparatus for starting up an n-phase, m-pole (n and m are integers) brushless motor (10) without use of physical rotary position detectors, such as Hall elements, comprising: phase energising signal generating means (24) for generating phase energising signals at a relatively low frequency and for generating phase energising signals at a relatively higher frequency to select respective phases for energisation; motor drive current means for supplying motor drive currents to those phases of said the selected for energisation; means for increasing the magnitude of the motor drive currents in a ramp-like manner over a first predetermined time period from a relatively low reference level to a motor drive level; and means for controlling the frequency of the phase energising signals to remain at the relatively low frequency during the first predetermined time period and to increase over a second predetermined time period to the relatively higher frequency.

Claim 38

Apparatus for starting up an n-phase, m-pole (n and m are integers) brushless motor (10) without use of physical rotary position detectors, such as Hall elements, comprising: phase energising signal generating means (24) for generating phase energising signals at a relatively low frequency and for generating phase energising signals at a relatively higher frequency to select respective phases for energisation; motor drive current means for supplying motor drive currents to those phases of said the selected for energisation; means for increasing the magnitude of the motor drive currents in a ramp-like manner over a first predetermined time period from a relatively low reference level to a motor drive level; and means for controlling the frequency of the phase energising signals to remain at the relatively low frequency during the first predetermined time period and to increase over a second predetermined time period to the relatively higher frequency.