Electronic motor controls, laundry machines including such controls and/or methods of operating such controls

Abstract

A control apparatus and method for an electric motor having sensing devices which sense the frequency and polarity of EMFs in the rotor windings down to a condition where the rotor is in condition for reversing, and causing reversing of the motor when the frequency is such as to allow reversing and the polarits polarity of a selected winding is at or near a zero crossing between positive and negative polarities. Cyclical reversal is effected by measuring the time the rotor takes to coast from a "power off" condition to the condition for reversing and with an electronically commutated motor reversing can usually be effected in one commutation period. The motor is used in a clothes washing machine or similar application where rapid reversal is required or timing of the time from one reversal to the next is required to be constant.

Description

., remainvariably variable stroke time operation.

Thus where the stroke time is to be variable according to the load in the washing tub and referring to FIG. 9a, which is similar to FIG. 9, the acceleration time 81 plus the plateau time 82 are set by the operator according to a required gentleness or vigorousness of washing to a fixed "power on" time. A small load will give a coast time indicated between points 83 and 84 with a delay curve 85. A large load gives a steeper delay curve 86 with a coast time indicated between points 83 and 87 and accordingly the motor will be in condition for reversal much earlier than in the light load coast time curve 85. If reversing is thus effected with a shortened stroke time more consistent washing performances will be obtained, whether the load is small or large.

Claims

1. A method of cyclically reversing an electronically commutated motor having a plurality of windings on a stator and a rotor having magnetic poles rotatable relative to said stator and using electronic control apparatus and means to indicate the position of the rotor, said method comprising the steps of

(a) initiating and then continuing a correct sequence of the commutations selected from a desired time of and desired number of the commutations,

(b) removing all the power from the windings and allowing the rotor to coast towards zero speed of rotation,

(c) testing and establishing a position of the rotor relative to the stator at least during a later part of the coasting of the rotor, and

(d) when the rotor has slowed to a condition in which application of reversed commutation will cause reversal of rotation but is still rotating (condition for reversing) and its position relative to the stator is established, and without delay after the condition for reversing, applying power to the stator windings and effecting entry into said correct sequence of the commutations of power to the winding, the position of entry into said correct sequence being determined by the direction of rotation of the rotor before stopping and the position of the rotor relative to the stator to cause the rotor to change direction the correct sequence of commutations follows automatically to maintain rotor rotation in the changed direction, and repeating steps (b) to (d) to give cyclical reversal for a desired time.

2. A method as claimed in claim 1 which includes the steps of indicating the direction and sequence of back EMFs in said windings after power has been removed therefrom and at least as the rotor nears a position where it is in the checking voltage transition points between positive and negative in at least one of said windings caused by the back EMFs in said at least one of said windings and the step of applying power and effecting entry comprises the step of entering the sequence of the commutations to cause reversal about a time when such a voltage transition point occurs in a selected winding.

3. A method as claimed in claim 1 or claim 2 wherein the step of testing and establishing includes the steps of testing back EMF from at least one of the windings for polarity and frequency, and wherein the step of applying power and effecting entry comprises the step of entering the sequence of the commutations when the frequency of the back EMF has fallen to a value such that the rotor has slowed to the condition for reversing and polarity is substantially at a zero crossing between opposite polarities in a selected winding.

4. A method as claimed in claim 3 in which the step of testing and establishing includes the step of testing all the windings to indicate the position of the rotor.

5. A method as claimed in claim 1 wherein the change in the sequence of the commutation usually occurs within a single commutation to cause a change in direction of rotation of the rotor.

6. A method for driving an electronically commutated motor cyclically in opposite directions during each of a sequence of half cycles, each half cycle comprising the steps of

applying electrical power driving the motor in a reverse direction from the prior cycle causing acceleration of the motor towards a desired speed, switching power off to the motor and reducing the speed of the motor to a condition where applying power in the next half cycle will reverse the direction of motor rotation,

determining resistance to rotation of the motor, and

adjusting the power applied to the motor in the step of applying power so as to cause acceleration of the motor in accordance with the resistance to motor rotation determined during the prior half cycle.

7. control apparatus for applying power to an electronically commutated motor having a plurality of windings on a stator adapted to be selectively commutated and a rotor having magnetic poles rotatable relative to said stator, said control apparatus comprising:

(a) timing means to time the period of one of the rotation and counting means to count the number of rotations of the rotor in a desired direction,

(b) commutation switching means to disconnect the power from said windings to allow the rotor to coast towards zero speed of rotation,

(c) detecting means to indicate rotor position relative to said stator at least during a later part of the coasting of the rotor before the rotor comes to rest, and

(d) pattern reverse means operable, in response to a signal from said detecting means when the rotor has slowed to a condition in which application of reversing commutations will cause reversal of rotation but is still rotating (condition to be reversed) and without delay after the condition to be reversed, for applying power to the stator windings and effecting entry into a correct sequence of the commutations of power to the winding, the position of entry into said correct sequence being determined by the direction of rotation of the rotor before stopping and the position of the rotor relative to the stator and thereby cause said rotor to change direction without testing for rotor direction.

8. control apparatus as claimed in claim 7 wherein said detecting means detects the direction and sequence of back EMFs in at least one of said windings after the power has been removed therefrom and detectts detects voltage transition points between positive and negative polarity in at least one of the windings and said pattern reverse means is actuated to reverse the sequence of the commutations about the time when a voltage transition point occurs in at least one of the windings.

9. control apparatus as claimed in claim 7 or claim 8 wherein said control apparatus further comprises:

(e) a commutating circuit responsive to control signals to cause electrical power from a power source to be applied commutatively to said windings to cause said rotor to rotate in a desired direction,

(f) testing means responsive to any back EMF generated in at least one unpowered winding to test the polarity and frequency of any back EMF generated in that unpowered winding,

(g) the pattern reversing reverse means comprising commutation reversing means to cause the commutation to reverse to give the correct sequence of commutation to rotate the rotor in the desired direction, and

(h) commutation reversing actuating means to reverse the commutation when said frequency is at a value such that the motor is in the condition to be reversed and the polarity in a selected winding is substantially at a zero crossing between opposite polarities.

10. electrical control means for cyclically controlling the supply of electrical power to an electric motor having a rotor, said control means comprising switching means to switch power on and off to said motor, power on timing means to time the length of power on time when power is switched on, coasting timing means to time the length of coasting time said rotor takes from the time power is switched off thereto to the time when said rotor has slowed to a condition in which the rotor rotation may be reversed (condition for reversing), the control means controlling the amount of power applied to the motor in accordance with the coast time, and reversing means to reverse the direction of said rotor when said rotor is in the condition for reversing and to switch power by said switching means when reversing is to be effected.

11. electrical control means as claimed in claim 10 further comprising power on timing means to time the length of power on time when power is switched on, wherein a stroke time during which said rotor rotates in one direction between reversals is the sum of said power on time and said coasting time.

12. A method of cyclically controlling power to an electrical motor having a rotor, said method including the steps of starting rotation of said rotor in one direction, setting an initial power on time and applying power to said motor during said power on time, switching off power at the end of said initial power on time, allowing the rotor to slow until the rotor has slowed to a condition in which application of power will cause reversal of rotation (condition to be reversed), checking a ramp down time after power is switched off within which the rotor slows to the condition to be reversed, causing reversal of direction of rotation of said rotor, as soon as the rotor is in the condition to be reversed, and repeating the preceding steps, using the ramp down time to adjust the amount of power applied to the motor while repeating the steps.

13. A method of cyclically controlling the supply of power to an electric motor having a rotor, said method including the steps of

setting a desired time of rotation of said rotor in one direction,

starting rotation of said rotor in said one direction,

setting an initial power on time and applying power to said motor during said initial power on time,

switching off the power to the motor at the end of said initial power on time, allowing the rotor to slow to a condition in which application of power to the motor will cause reversal of rotation but is still rotating (condition for reversal),

checking a ramp down time within which the rotor takes to slow to the condition for reversal,

causing reversal of direction of rotation of said rotor by applying power to the motor, substantially at said condition for reversal, for a further power on time which is such that said further power on time plus said ramp down time (half cycle time) equals said desired time,

switching off power to said motor at the end of said further power on time, again checking the next said ramp down time within which the rotor takes to slow the condition for another reversal,

again reversing direction of the rotor when said rotor is in the condition for reversal and applying power to said motor for a still further power on time which is such that said still further power on time plus said next down ramp time (half cycle time) equals said desired time and repeating the steps, starting with the step of causing reversal of direction, for a desired length of time, adjusting the power on time during at least one said half cycle time in accordance with a previous ramp down time at desired intervals of time so that the adjusted power on time for the at least one said half cycle time plus the ramp down time for the previous half cycle time equals said desired time.

14. A method of electronically cyclically controlling the supply of power to an electric motor using sensing means and actuate adjustment means for adjusting the power to the motor, said method including the steps of setting a desired speed of rotation of the motor, sensing the resistance to rotation of the motor; using responses from the sensing means for controlling the adjustment means to adjust the power supplied to the motor to change the motor speed towards said desired speed and then operate the motor within a range of speeds substantially at said desired speed of rotation, switching off the supply of power to the motor following which the motor slows to a stop and applying power to the motor and repeating the recited steps at least once, starting with the step of controlling to thereby cause a change in the adjusted power supplied to the motor in accordance with the sensed resistance to rotation of the rotor that occurred prior to the stop of the motor, with the motor running in the reverse direction.

15. A method as claimed in claim 14 which includes the step of sensing resistance to rotation by measuring the time the motor takes to run down from a power off condition to a condition in which application of power to the motor will cause reversal of rotation (condition to be reversed).

16. A method as claimed in claim 14 or claim 15 which includes wherein the step of controlling initially causes acceleration of the motor to just below the desired speed and, after stopping of the motor, causes acceleration of the motor at least substantially up to the desired speed.

17. A method as claimed in claim 14 or claim 15 wherein the step of using responsive responses for controlling causes the motor, after stopping, to accelerate to a speed just above the desired speed and thereby overshoot the desired speed and then fall to the desired speed.

18. A method as claimed in claim 15 wherein the step of using responsive responses for controlling causes the motor speed, after stopping, to overshoot or undershoot in relation to a desired plateau level of the desired speed to give a desired vigorousness of motion to the motor.

19. A method as claimed in any one of claims 12 to 15, wherein the motor has windings on a stator driving a rotor, which method includes the steps of

(a) continuing motor rotation for a desired time, or angle or of rotation,

(b) removing all power from the windings and allowing the rotor to coast towards a condition to be reversed,

(c) testing the position of the rotor relative to the stator during the coasting towards the condition to be reversed, and

(d) when the rotor is in a condition such that application of power to the windings will cause reversal of rotation (condition to be reversed) and its position relative to the stator is known, applying a changed sequence of commutations to the windings to cause the rotor to change direction, the correct commutations following automatically to maintain rotor rotation in the changed direction, and repeating the steps to give cyclical reversal for a desired time.

20. A method as claimed in claim 19, which includes the steps of following the direction and sequence of back EMFs in said windings after power has been removed therefrom and at least as the rotor nears a position where it is in the condition to be reversed, checking the voltage transitions points between positive and negative for at least one of said windings and changing the sequence of commutations to the windings to cause reversal about the time when a voltage transition point occurs in at least one said winding.

21. A method as claimed in claim 20 which includes the steps of testing the back EMFs from at least one said winding for polarity and frequency and changing the sequence of commutation when the frequency has fallen to a value such that the rotor is in the condition to be reversed and the polarity is at or near a zero crossing between opposite polarities in at least one said winding.

22. A method as claimed in claim 21 which includes the step of testing all the windings to indicate the position of the rotor.

23. A method as claimed in claim 22 comprising the step of enabling said changed sequence of commutations to occur within a single commutation change to cause a change in direction of rotation of the rotor.

24. An electrical control means for cyclically controlling the supply of electrical power to an electric motor having a rotor, said control means comprising

switching means to switch power to said motor on and off,

power timing means to control the length of time when power is switched for a selected power on time,

coasting timing means to time the length of the coast time said rotor takes from the time power is switched off thereto to the time when said rotor is in condition for reversal of direction of rotation,

stroke time setting means to set, to a desired value, the stroke time during which said rotor rotates in one direction between reversals,

algebraic subtracting means to algebraically subtract a previous coast time from said stroke time to arrive at a time setting for said selected power on time,

reversing means to reverse the direction of said rotor when said rotor is in condition for reversal.

25. An electrical control means for cyclically controlling the supply of electrical power to an electrical motor having a rotor, said control means comprising:

switching means to switch power to said motor on and off, coasting timing means to time the length of time said rotor takes from the time power is switched off thereto to the time when said rotor has slowed to a condition in which the rotor direction may be reversed (condition for reversing), reversing means to reverse the direction of said rotor when said rotor is in the condition for reversing and to switch on said switching means when reversing is to be effected, and means for controlling the supply of power to said motor in accordance with a desired length of time of coasting to the condition for reversing.

26. An electrical control means for cyclically controlling the supply of electrical power to an electric motor having a rotor, said electrical control means including setting means operable to set a desired speed of rotation of the rotor of said motor, sensing means to sense resistance to rotation of the rotor prior to a reversal in direction of running of the rotor, adjustment means responsive to the resistance to rotation speed prior to a preceding reversal of running of the rotor for adjusting the power supplied to the motor to accelerate said rotor towards the desired speed and to maintain the rotor speed within a range of speeds substantially at said desired speed of rotation, switching means to switch off the supply of power to said motor after a desired time and reversing means, operable when said rotor has slowed to a condition in which the rotation direction may be reversed (condition for reversing), to reenable the preceding recited means with the rotor running in the reverse direction.

27. electrical control means as claimed in claim 26 wherein said sensing means comprises timing means to measure the time the rotor takes to run down from a powr power off condition to the condition for reversing.

28. electrical control means as claimed in claim 26 wherein the motor has a rotor stator including windings; said electrical control means includes including:

(e) a commutating circuit responsive to control signals to cause electrical power from a power source to be applied commutatively to said windings and to cause said rotor to rotate in a desired direction,

(f) testing means responsive to any back EMF generated in at least one unpowered winding to test the frequency and polarity of the back EMF generated in that unpowered winding,

(g) the reversing means comprising commutation reversing means to reverse commutation of the commutatively applied electric power to give a correct sequence of commutation to rotate the rotor in the desired direction when the condition for reversing exists and a selected winding has a signal therein substantially at a zero crossing between opposite polarities.

29. electrical control means as claimed in claim 26 or claim 27 wherein the motor has a stator including windings to drive the rotor; said electrical control means including means for providing commutation signals to the windings, and said reversing means comprising

(a) counting means to count one of the time of the period of rotation and the number of rotations of the rotor in a desired direction,

(b) communication commutation switching means to disconnect the power from said windings,

(c) detecting means to indicate rotor position relative to said stator, and

(d) pattern reverse means operable by a signal from said detecting means to cause commutation signal changes to the windings which cause said rotor to change direction without testing for rotor rotational direction.

30. electrical control means as claimed in any one of claims 25 to 27 wherein the motor has windings, and comprising braking means to brake the rotor, the braking means comprising switching means, having an impedance, to connect an end of at least one winding to an end of at least one other winding to provide a closed circuit through said impedance and the interconnected windings through which braking currents pass, the other ends of the interconnected windings being connected together, and comparator means interconnected to compare voltages between opposite ends of the windings to enable the speed of the rotor during braking to be indicated.

31. electrical control means as claimed in any one of claims 25 to 27 wherein the motor has a stator including windings; said electrical control means further comprising braking means for braking the rotor, the braking means comprising swiching means, having an impedance, to connect one end of one winding to one end of another of said windings through said impedance, the other end of said windings being connected together, comparator means for comparing the voltages between opposite ends of the windings to enable the speed of the rotor during braking to be established.

32. A method of cyclically reversing an electronically commutated motor having a plurality of windings on a stator and a rotor having magnetic poles rotatable relative to said stator, said method comprising the steps of

(a) removing substantially all the power from the windings and, while the rotor is rotating, allowing the rotor to coast towards zero speed of rotation, and

(b) when the rotor has slowed to a condition in which application of a reversed commutation will cause reversal of rotation at any time between a still rotating condition of the rotor and substantially the time the rotor has stopped rotation (condition for reversing) and without delay, applying power to the stator windings and effecting entry at the correct sequence of commutations of power to the windings to cause the rotor to change direction and to maintain rotor rotation in the changed direction.

33. The method of claim 32 comprising the step of repeating the recited steps to provide cylical reversals for desired time intervals.

34. The method of claim 33 comprising the steps of

testing and determining the position of the rotor relative to the stator at a later part of the coasting of the rotor before reaching zero speed of rotation, the step of effecting entry into the correct sequence of commutations being condition conditioned upon the determined position in the preceding step.

35. A method of cyclically controlling the supply of power to an electric motor having a rotor, a stator and windings, which method comprises:

(a) setting a desired time of rotation of said rotor in one direction,

(b) starting rotation of said rotor in said one direction, setting an initial "power on" time during which power is applied to said motor, switching off power at the end of said initial "power on" time, causing the rotor to slow to a condition for reversing while the rotor is still rotating (condition for reversal),

(c) checking a ramp down time which said rotor takes to slow to said condition for reversal,

(d) causing reversal of direction of rotation of said rotor,

(e) applying power to said motor for a further "power on" time which is such that said further "power on" time plus said ramp down time (half cycle) equals said desired time,

(f) switching off power to said motor at the end of said further "power on" time,

(g) checking the next ramp down time and reversing direction of the rotor to said one direction when said rotor is in said condition for reversal,

(h) applying power to said motor for a still further "power on" time which is such that said further "power on" time plus said next ramp down time substantially equals said desired time, and

(i) selectively repeating selected ones of the preceding steps for a desired length of time, adjusting the "power on" time at desired intervals of time so that the adjusted "power on" time for a further half cycle plus the ramp down time for a previous half cycle substantially equals said desired time.

36. The method of claim 35 wherein the condition for reversal is one wherein a reversal in commutation of power to the windings will cause a reversal of rotation of the rotor.

37. A method according to claim 35, including the steps of:

(a) setting a desired speed of rotor rotation,

(b) setting a forward cycle comprising

(i) applying power to said motor at an initial rate for a predetermined period to accelerate the rotor,

(ii) determining the speed attained at the end of the period of acceleration, which speed depends on the resistance to rotation of the rotor, and

(iii) switching off the power supply to the motor,

(c) setting a reverse cycle comprising repeating the forward cycle steps, but with the rotor running in the reverse direction and with the power adjusted in accordance with the previously determined speed to adjust the acceleration rate and thereby change the rotor speed so that it approaches a desired speed, and

(d) selectively repeating the forward and reverse cycles.

38. A method according to claim 35 or 37, which includes the further step of sensing rotor resistance to rotation by measuring the time the rotor takes to run down from a power off condition when power is switched off to the condition for reversal.

39. A method according to claim 37 comprising the steps of effecting such acceleration to cause the rotor to rotate initially just below a desired speed and adjusting the supply of power to the motor so that the rotor speed rises to said desired speed.

40. A method according to claim 37 further comprising the steps of effecting such acceleration to cause the rotor to accelerate to a speed just above a desired speed and adjusting the power supplied to the motor so that the speed falls to the desired speed.

41. A method according to claim 35 or 37 further comprising the steps of adjusting a level of one of overshoot and undershoot in speed of the rotor in relation to a desired plateau level of constant speed to give a desired vigorousness of motion to the rotor.

42. A method according to claim 35 or 37 comprising

initiating and then continuing a correct sequence of commutations of power to the windings selected from a desired time of and a desired number of commutations,

a reversing cycle comprising removing all the power from the windings and allowing the rotor to coast towards zero speed of rotation,

testing and establishing the position of the rotor relative to the stator at least during a latter part of the coasting of the rotor, and

when the rotor has slowed to a condition in which application of reversed commutation will cause reversal of rotation but is still rotating and the position of the rotor relative to the stator is known, without delay applying power to the windings effecting entry into the correct sequence of commutations, the position of entry into the correct sequence being determined by the direction of rotation of the rotor before stopping and the position of the rotor relative to the stator, to cause the rotor to change direction, the correct sequence of commutations following automatically to maintain rotor rotation in the changed direction, and

selectively repeating the reversing steps to achieve cyclical reversal for a desired time.

43. A method according to claim 42 comprising following the direction and sequence of EMFs in said windings after power has been removed therefrom and, at least as the rotor approaches a position where it is in condition for reversal, checking the voltage transition points between positive and negative for at least one winding and changing the sequence of commutations to cause reversal substantially at the time when a voltage transition point occurs in a selected winding.

44. A method according to claim 43 further comprising testing the EMFs from at least one winding for polarity and frequency and changing the sequence of commutations when the frequency has fallen to a value such that the rotor is in condition for reversal and the polarity is substantially at a zero crossing between opposite polarities.

45. A method according to claim 44 wherein the step of testing comprises testing all the windings to indicate the position of the rotor.

46. A method according to claim 42 further comprising a step of enabling the sequence of commutations to occur within a single commutation change to cause a change in direction of rotation of the rotor.

47. A method according to claim 42 wherein the motor is an electronically commutated motor.

48. A method according to claim 35 or 36 wherein the desired time is variable.

49. A method of electronically cyclically controlling the supply of power to an electric motor, having a rotor, which method comprises the steps of

(a) a forward cycle comprising

(i) setting a desired speed of rotation for the rotor,

(ii) applying power to said motor at an initial rate for a predetermined period to accelerate the rotor, and

(iii) determining the speed attained at the end of the predetermined period of acceleration, which speed depends on the resistance to rotation of the rotor, and switching off the power supply to the motor, and

(b) a reverse cycle comprising repeating the forward cycle steps, but with the rotor running in the reverse direction and with the power adjusted in accordance with the previously determined speed to adjust the acceleration rote of the rotor and thereby change the rotor speed towards a desired speed.

50. A method according to claim 49 further comprising the steps of

sensing resistance of the rotor to rotation by setting an acceleration rate,

sensing the speed of the rotor obtained in a given time period, and

comparing the obtained speed with said desired speed of rotation and adjusting the power applied in the step of applying power during a next cycle, to achieve an acceleration rate which will accelerate the rotor closer to the desired speed.

51. A method according to claim 49 or 50, further comprising the steps of effecting acceleration causing the rotor to rotate initially just below the desired speed during one of said cycles and adjusting the application of power so that the speed rises to said desired speed in a later one of said cycles.

52. A method according to claim 49 or claim 50, further comprising the steps of effecting acceleration to cause the rotor to accelerate to a speed just above the desired speed and adjusting the application of power so that the speed falls to said desired speed.

53. A method according to claim 49 or 50, further comprising the step of adjusting acceleration of the rotor so as to cause one of an overshoot and undershoot in rotor speed in relation to the desired rotor speed after acceleration to give a desired vigorousness of motion to the rotor.

54. A method according to claim 49 or 50 wherein the motor further comprises a stator and windings and further comprising the steps of

a) initiating and then continuing a correct sequence of commutations of power to the windings selected from a desired time of and a desired number of commutations, causing the rotor to rotate in one direction,

b) reversing all of the power from the windings and allowing the rotor to coast towards zero speed or rotation,

c) testing and establishing a position of the rotor relative to the stator at least during a latter part of the coasting of the rotor, and

d) when the rotor has slowed to a condition in which application of reversed commutation will cause reversal of rotation but the rotor is still rotating and the position of the rotor relative to the stator is known, without delay applying power to the windings effecting entry into the correct sequence of commutations, the position of entry into the correct sequence being determined by the direction of rotation of the rotor before stopping and the position of the rotor relative to the stator, to cause the rotor to change direction, the correct sequence of commutations following automatically to maintain rotor rotation in the changed direction, and repeating the steps of removing power and testing and establishing, and without delay applying power to give cyclical reversals in direction of rotation of the rotor for a desired time.

55. A method according to claim 54, further comprising the steps of following the direction and sequence of voltage representing EMFs in said windings after power has been removed therefrom and, at least as the rotor nears a position where it is in condition for reversal, checking the voltage transition points between positive and negative for each winding and changing the sequence of commutations to cause reversal about the time when a voltage transition point occurs in a selected winding.

56. A method according to claim 55, further comprising the steps of testings the voltage representing EMFs from at least one of the windings for polarity and frequency and changing the sequence of commutation when the frequency has fallen to a value such that the rotor is in condition for reversing and the polarity is substantially at a zero crossing between opposite polarities in a selected winding.

57. A method according to claim 56 wherein the step of testing comprises testing all of the windings.

58. A method according to claim 55 further comprising a step of enabling the change in the sequence of commutations to occur within a single commutation change to cause a change in direction or rotation of the rotor.

59. A method according to claim 49 wherein the motor is an electronically commutated motor and the recited steps are applied to such motor.

60. An electronic controller for cyclically controlling the supply of electrical power to an electric motor having a rotor, a stator and windings, comprising

a) setting means operable to set a desired speed of rotation of the rotor,

b) means for setting an initial rate of supply of power and applying that rate of power to said motor for a predetermined period to accelerate said rotor to attain an initial speed and to substantially maintain that speed,

c) speed determining means for determining said initial speed which speed is dependent on the resistance to rotation of said rotor,

d) switching means to switch off the supply of power to said motor after said predetermined period,

e) adjusting means responsive to said speed determining means for adjusting the supply of power to the motor in accordance with the previously attained speed to adjust the acceleration rate and thereby change said initial rotor speed towards a desired speed, and

f) reversing means operable when said rotor is in a condition for reversal for causing cycles of forward and reverse rotor rotation to be repeated.

61. An electronic controller according to claim 60 further comprising sensing means for sensing resistance to rotation of the rotor, said sensing means comprising timing means to measure the time the rotor takes to run down from switching power off to the motor to the condition for reversal.

62. An electronic controller according to claim 60 or 61, wherein the reversing means comprises

a) switching means to disconnect power from said windings to allow the rotor to run down towards zero speed of rotation,

b) detecting means to test, establish and indicate rotor position relative to said stator, and

c) pattern reverse means operable in response to a signal from said detecting means, when the rotor has slowed to a condition in which application of reversed commutation will cause reversal of rotation but the rotor is still rotating, for issuing control signals to effect entry into a sequence of commutations to cause said rotor to change direction without testing for rotor direction.

63. An electronic controller according to claim 62 wherein the reversing means further comprises one of timing means to time the period of rotation and counting means to count the number of rotations of the rotor in a desired direction.

64. An electronic controller according to claim 60 or 61, further comprising

a) a commutating circuit responsive to control signals to cause electrical power from a power source to be applied commutatively to said windings for causing said rotor to rotate in a desired direction,

b) testing means responsive to any EMF generating in at least one unpowered winding to test the frequency and polarity of EMFs generated in that unpowered winding, and

c) commutation reversing means for reversing commutation to give the correct sequence of commutation to rotate the rotor in the desired direction when the frequency has fallen to a value at which the rotor is in condition for reversal and the polarity of a selected winding is substantially at a zero crossing between opposite polarities.

65. An electronic controller according to claim 60, further comprising braking means to brake the rotor, the braking means comprising switching means, having an impedance, for connecting one end of one winding to one end of another of said windings through said impedance, the other ends of said windings being connected together, and comparator means for comparing the voltages between opposite ends of the windings for establishing the speed of the rotor during braking.

66. An electronic controller according to claim 60, wherein said electronic controller is adapted for controlling an electronically commutated motor.

67. An electrical control for cyclically controlling the supply of electrical power to an electric motor having a rotor, a stator and windings, said electrical control comprising

switching means for switching power to said motor on and off,

power timing means for controlling the length of the power on time,

coast timing means for timing the length of time said rotor takes from the time power is switched off thereto to the time when said rotor is in a condition for reversal of direction of rotation,

stroke time setting means for setting a desired value of the stroke time during which said rotor rotates in one direction between reversals,

algebraic subtracting means for algebraically subtracting a previous coast time from said stroke time to yield a result corresponding to a time setting for said power on time,

reversing means for reversing the direction of said rotor when said rotor is in the condition for reversal and for switching on said switching means when reversal is to be effected, and

means for repeating the operation thereof, enabling selected ones of the previously recited means for a desired length of time.

68. electrical control according to claim 67, further comprising means for providing commutation signals to the windings, and wherein the reversing means comprises

counting means for counting the time of the period of rotation or the number of rotations of the rotor in a desired direction,

commutation switching means for disconnecting power from said windings,

detecting means for indicating rotor position relative to said stator, and

pattern reverse means responsive to a signal from said detecting means for issuing control signals to cause commutation signal changes to the windings which cause said rotor to change rotational direction without testing for rotor rotational direction.

69. electrical control according to claim 68 further comprising

a commutating circuit responsive to said control signals for causing electrical power from a power source to be applied commutatively to said windings for causing said rotor to rotate in a desired direction,

testing means responsive to any EMF generated in at least one unpowered winding to test the frequency and polarity of EMFs generated in that unpowered winding, and

the pattern reversing means comprising commutation reversing means to reverse commutation to give the correct sequence of commutation to rotate the rotor in the desired direction when the frequency has fallen to a value at which the rotor is in condition for reversal and polarity in the unpowered winding is substantially at a zero crossing between opposite polarities.

70. electrical control according to claims 67, 68 or 69 comprising rotor braking means, the braking means comprising switching means, having an impedance, for connecting one end of one of said windings to one end of another of said windings through the impedance, the other ends of said windings being connected together, and comparator means for comparing the voltages between opposite ends of the windings for establishing the speed of the rotor during braking.

71. electrical control according to claim 70 wherein the stroke time setting means is variable.

72. electrical control means according to any one of claims 67, 68 or 69 comprising

setting means for setting a desired speed of rotation of the rotor,

means for setting and applying an initial rate of supply of power to said motor for a predetermined period of time to accelerate said rotor to attain an initial speed and to maintain that speed,

speed determining means for determining said initial speed dependent on the resistance to rotation of said rotor,

wherein the switching means is adapted for switching off the supply of power to said motor after said predetermined period of time,

adjusting means responsive to said speed determining means for adjusting the supply of power in accordance with the previously attained rotor speed to adjust the acceleration rate and thereby change said initial rotor speed towards a desired speed, and

the reversing means being operable when said rotor is in condition for reversal for selectively causing cycles of forward and reverse rotor rotation to be repeated.

73. electrical control according to claim 72 further comprising means for sensing resistance to rotation of the rotor, which means for sensing resistance comprises timing means for measuring the time the rotor takes to run down from a power off condition to the condition for reversal.

74. electrical control according to claim 68 wherein said detecting means comprises means for detecting the direction and sequence of EMFs in at least one of the windings after power has been removed therefrom and for detecting voltage transition points between positive and negative polarity, said pattern reverse means being operative for reversing the sequence of commutations substantially at the time when a voltage transition point occurs in said at least one winding.

75. electrical control according to claim 68 wherein said electric motor is an electronically commutated motor.

76. A method of cyclically reversing an electronically commutated motor having a plurality of windings on a stator and a rotor having magnetic poles rotatable relative to said stator to create back EMFs and using electronic control apparatus comprising a microprocessor, said method comprising the steps of:

(a) applying power to the motor to provide power to the windings to initiate and continue a sequence of commutations selected from a desired time of, and desired number of, the commutations;

(b) turning off power to the motor to remove all power from the windings and allow the rotor to coast toward zero speed of rotation;

(c) determining a direction in which the rotor is rotating using the back EMFs created by the rotor and windings;

(d) determining when the rotor has slowed sufficiently to be in a condition for reversal of direction by (i) sensing when the back EMFs are at a first reference value and sensing when the back EMFs reach a second reference value, (ii) determining that the rotor is in the condition for reversal if an elapsed time between the reference values is at least equal to a predetermined commutation time period, and (iii) if the elapsed time is less than the predetermined commutation time period, repeating the step (i) of sensing using new first and second reference values, and the step (ii) of determining, until the elapsed time is at least as great as the predetermined commutation time period; and

(e) reversing the rotor by reversing the sequence of commutations based on the rotor direction and using back EMFs as an indication of rotor position, when the rotor is in the condition for reversal.

77. The method of claim 76 wherein step (d)(ii) further comprises determining that the rotor is in the condition for reversal, where elapsed time from sensing the first reference value is at least as great as a predetermined minimum time period, without sensing the second reference value, the predetermined minimum time period being greater than the predetermined commutation time period.

78. The method of claim 77 further comprising the step of timing elapsed time from the turning off of power to motor, and applying dynamic braking to the rotor when the condition for reversal is not reached within a predetermined maximum time period.

79. The method of claim 78 wherein the predetermined minimum time period is 40 milliseconds, the predetermined commutation time period is 20 milliseconds, and the predetermined maximum time period is 150 to 200 milliseconds.

80. The method of claim 78 wherein the first and second reference values correspond to a first position of the rotor where one of the windings has its back EMF cross zero volts and a next position of the rotor where one of the windings has its back EMF cross zero volts, respectively.

81. The method of claim 76 further comprising the step of timing elapsed time from the turning off of power to the motor, and applying dynamic braking to the rotor when the condition for reversal is not reached within a predetermined maximum time period.

82. The method of claim 76 wherein the first and second reference values correspond to a first position of the rotor where one of the windings has its back EMF cross zero volts and a next position of the rotor where one of the windings has its back EMF cross zero volts, respectively.

83. The method of claim 82 further comprising the steps of indicating a direction and sequence of back EMFs in the windings after power has been removed therefrom and at least as the rotor nears a position where the rotor is in the condition for reversal, checking voltage transition points between positive and negative in at least one of the windings caused by the back EMFs in the at least one of said windings, and wherein the step of reversing further comprises applying power to the motor and effecting entry into a correct sequence of commutations to achieve reversal of the rotor, the sequence of the commutations being entered about a time when such voltage transition point occurs in a selected winding.

84. The method of claim 76 wherein, in the step (d)(iii) of repeating, the new first reference value corresponds to a previous second reference value.

85. The method of claim 76 wherein the rotor rotation direction is one of clockwise and counterclockwise, and the direction is determined by the sequence of back EMFs generated from the windings, and wherein reversal is effected by applying voltage to at least some of the windings which is opposite in polarity from the sequence of back EMFs.

86. The method of claim 85 wherein there are three windings connected to a common central point at a reference voltage, and the windings are spaced 120°, the three windings comprise a first winding (A), a second winding (B), and a third winding (C), and the step of reversing comprises applying a correct sequence of commutations to the windings to effect reversal, wherein if the rotor is rotating clockwise, power is applied to the windings to effect counterclockwise rotation, as follows:

if the back EMF from the first winding is positive (A+), and from the third winding is negative (C-), applying positive voltage (C+) across the third winding and negative voltage (A-) across the first winding,

if the back EMF from the second winding is positive (B+), and from the third winding is negative (C-), applying positive voltage (C+) across the third winding and negative voltage (B-) across the second winding,

if the back EMF from the second winding is positive (B+), and from the first winding is negative (A-), applying positive voltage (A+) across the first winding and negative voltage (B-) across the second winding,

if the back EMF from the third winding is positive (C+), and from the first winding is negative (A-), applying positive voltage (A+) across the first winding and negative voltage (C-) across the third winding,

if the back EMF from the third winding is positive (C+), and from the second winding is negative (B-), applying positive voltage (B+) across the second winding and negative voltage (C-) across the third winding,

if the back EMF from the first winding is positive (A+), and from the second winding is negative (B-), applying positive voltage (B+) across the second winding and negative voltage (A-) across the first winding, and

wherein if the rotor is rotating counterclockwise, power is applied to the windings to effect clockwise rotation, as follows:

if the back EMF from the first winding is negative (A-), and from the third winding is positive (C+), applying positive voltage (A+) across the first winding and negative voltage (C-) across the third winding,

if the back EMF from the second winding is negative (B-), and from the third winding is positive (C+), applying positive voltage (B+) across the second winding and negative voltage (C-) across the third winding,

if the back EMF from the second winding is negative (B-), and from the first winding is positive (A+), applying positive voltage (B+) across the second winding and negative voltage (A-) across the first winding,

if the back EMF from the first winding is positive (A+), and from the third winding is negative (C-), applying positive voltage (C+) across the third winding and negative voltage (A-) across the first winding,

if the back EMF from the second winding is positive (B+), and from the third winding is negative (C-), applying positive voltage (C+) across the third winding and negative voltage (B-) across the second winding, and

if the back EMF from the second winding is positive (B+), and from the first winding is negative (A-), applying positive voltage (A+) across the first winding and negative voltage (B-) across the second winding.

87. The method of claim 76 further comprising the step of determining a position of the rotor when the rotor is in the condition for reversal, to provide the indication of rotor position.

88. An apparatus for cyclically reversing an electronically commutated motor having a plurality of windings on a stator and a rotor having magnetic poles rotatable relative to said stator to create back EMFs, said apparatus comprising:

(a) power on means for applying power to the motor to provide power to the windings to initiate and continue a sequence of commutations selected from a desired time of, and desired number of, the commutations;

(b) commutation switching means for turning off power to the motor to remove all power from the windings and allow the rotor to coast toward zero speed of rotation;

(c) detection means for sensing back EMFs created by the rotor and windings and for providing an indication of a direction in which the rotor is rotating;

(d) means for determining when the rotor has slowed sufficiently to be in a condition for reversal of direction, comprising (i) first means for sensing when the back EMFs are at a first reference value and for sensing when the back EMFs reach a second reference value, (ii) second means for measuring an elapsed time for the back EMFs to reach the second reference value after passing the first reference value, and for determining that the rotor is in the condition for reversal when the elapsed time is at least equal to a predetermined commutation time period, and wherein the first means is adapted for repeating sensing, when the elapsed time is less than the predetermined commutation time period, using new first and second reference values, until the elapsed time is at least as great as the predetermined commutation time period; and

(e) means responsive to the means for determining when the rotor is in the condition for reversal for reversing the rotor by reversing the sequence of commutations based on the indication by the detection means of rotor direction and an indication of rotor position based on the back EMFs.

89. The apparatus of claim 88 wherein the second means further comprises means for determining that the rotor is in the condition for reversal when an elapsed time for sensing the first reference value is at least as great as a predetermined minimum time period without sensing the second reference value, the predetermined minimum time period being greater than the predetermined commutation time period.

90. The apparatus of claim 89 further comprising means for timing an elapsed time from the turning off of power to the motor, and means for applying dynamic braking to the rotor when the condition for reversal is not reached within a predetermined maximum time period.

91. The apparatus of claim 90 wherein the predetermined minimum time period is 40 milliseconds, the predetermined commutation time period is 20 milliseconds, and the predetermined maximum time period is 150 to 200 milliseconds.

92. The apparatus of claim 90 wherein the first and second reference values correspond to a first position of the rotor where one of the windings has its back EMF cross zero volts and a next position of the rotor where one of the windings has its back EMF cross zero volts, respectively.

93. The apparatus of claim 88 further comprising means for timing an elapsed time from the turning off of power to the motor, and means for applying dynamic braking to the rotor when the condition for reversal is not reached within a predetermined maximum time period.

94. The apparatus of claim 88 wherein the first and second reference values correspond to a first position of the rotor where one of the windings has its back EMF cross zero volts and a next position of the rotor where one of the windings has its back EMF cross zero volts, respectively.

95. The apparatus of claim 94 wherein the detection means senses the sequence of back EMFs in the windings after power has been removed therefrom and at least as the rotor nears a position where the rotor is in the condition for reversal, the detection means comprises means for checking voltage transition points between positive and negative in at least one of the windings caused by the back EMFs in the at least one of said windings and wherein the means for reversing comprises means for applying power to the motor and effecting entry into a correct sequence of commutations to achieve reversal of the rotor about a time when a voltage transition point occurs in a selected winding.

96. The apparatus of claim 88 wherein the new first reference value corresponds to a previous second reference value.

97. The apparatus of claim 88 wherein rotor rotation direction is one of clockwise and counterclockwise, the detection means is adapted for determining rotor direction by the sequence of back EMFs generated from the windings, and the means for reversing effects reversal by applying voltage to at least some of the windings which voltage is opposite in polarity from the sequence of back EMFs.

98. The apparatus of claim 97 wherein there are three windings connected to a common central point at a reference voltage, and the windings are spaced at 120°, the three windings comprise a first winding (A), a second winding (B), and a third winding (C), and wherein in response to the detection means sensing that the rotor is rotating clockwise, the means for reversing applies power to the windings to effect counterclockwise rotation, as follows:

if the back EMF from the first winding is positive (A+), and from the third winding is negative (C-), applying positive voltage (C+) across the third winding and negative voltage (A-) across the first winding,

if the back EMF from the second winding is positive (B+), and from the third winding is negative (C-), applying positive voltage (C+) across the third winding and negative voltage (B-) across the second winding,

if the back EMF from the second winding is positive (B+), and from the first winding is negative (A-), applying positive voltage (A+) across the first winding and negative voltage (B-) across the second winding,

if the back EMF from the third winding is positive (C+), and from the first winding is negative (A-), applying positive voltage (A+) across the first winding and negative voltage (C-) across the third winding,

if the back EMF from the third winding is positive (C+), and from the first winding is negative (B-), applying positive voltage (B+) across the second winding and negative voltage (C-) across the third winding,

if the back EMF from the first winding is positive (A+), and from the second winding is negative (B-), applying positive voltage (B+) across the second winding and negative voltage (A-) across the first winding, and

wherein in response to the detection means sensing that the rotor is rotating counterclockwise, the means for reversing applies power to the windings to effect clockwise rotation, as follows:

if the back EMF from the first winding is negative (A-), and from the third winding is positive (C+), applying positive voltage (A+) across the first winding and negative voltage (C-) across the third winding,

if the back EMF from the second winding is negative (B-), and from the third winding is positive (C+), applying positive voltage (B+) across the second winding and negative voltage (C-) across the third winding,

if the back EMF from the second winding is negative (B-), and from the first winding is positive (A+), applying positive voltage (B+) across the second winding and negative voltage (A-) across the first winding,

if the back EMF from the first winding is positive (A+), and from the third winding is negative (C-), applying positive voltage (C+) across the third winding and negative voltage (A-) across the first winding,

if the back EMF for the second winding is positive (B+), and from the third winding is negative (C-), applying positive voltage (C+) across the third winding and negative voltage (B-) across the second winding, and

if the back EMF from the second winding is positive (B+), and from the first winding is negative (A-), applying positive voltage (A+) across the first winding and negative voltage (B-) across the second winding.

99. The apparatus of claim 88 further comprising means for determining a position of the rotor when the rotor is in the condition for reversal, to provide the indication of rotor position.