Method and apparatus for DC motor speed control

A method of controlling an electronically commutated motor having a stator, at least one winding phase, a permanent magnet rotor, and rotor position sensing means for producing a commutation signal information after each predetermined angle of rotor rotation, comprising the following steps:

• a) obtaining a commutation time value (KZalt) from one of
• loading an arbitrary commutation time value (Kzalt) stored in a memory, and
• determining a commutation time value (Kzalt) substantially corresponding to a time period between a preceding commutation signal information and a present commutation signal information;
• b) based on said obtained commutation time value, making an estimate of a first future point in time at which a subsequent commutation time signal is likely to occur by assuming that the distance of said subsequent commutation signal information from the present commutation signal information will correspond to said obtained commutation time value;
• c) making an estimate of a second future point in time by subtracting, from said first estimated point in time, a value corresponding to a predetermined length of time (D), said second future point in time (KZ'alt) being closer to the present commutation signal information than said first future point in time;
• and
• d) switching off energization of an energized winding phase when said second point in time (KZ'alt) is reached so that said energization is interrupted before said subsequent commutation signal information appears.

A method of regulating the rotational speed of an electronically commuted motor having a rotor, a stator, and a control circuit adapted to recognize, and to respond to,

• a predetermined speed-too-low condition and
• a predetermined speed-too-high condition, comprising the following steps:
• a) Responsive to a speed-too-low condition, first control steps are carried out at least partially in at least one first predetermined rotational position range of the rotor;
• b) Responsive to a speed-too-high condition, second control steps are carried out at least partially in at least one second predetermined rotational position range of the rotor,
• the second rotational position range being different from the first rotational position range.

A method for monitoring the speed of an electronically commutated motor having a rotor, a stator comprising a stator winding, and a control circuit controlling current flowing in said stator winding,

• said control circuit successively executing, in operation, program loops of predetermined duration, comprising the following steps:
• a) counting, beginning substantially at a first rotational position of said rotor, and ending substantially at a point in time when said rotor has rotated through a predetermined angle from said first rotational position, how many program loops have been executed;
• b) monitoring continuously the count of said program loops executed, by program elements contained in said loop;
• c) interrupting motor current for a predetermined time interval when said count exceeds a predetermined value,;
• and
• d) attempting to restart the motor after the predetermined time interval has elapsed.

An electronically commutated DC motor comprising a stator, a rotor, and a control circuit for controlling its rotational speed of said motor, comprising:

• a) A capacitor, means for changing a voltage on said capacitor as a function of time, means for starting said voltage change when a first, predetermined rotational position of the rotor is reached;
• b) a comparator, where this voltage is compared to a predetermined second voltage to produce a reference signal (U.sub.dif) when a predetermined reference criterion is satisfied;
• c) a measuring component to measure the difference in time (+T.sub.d, -T.sub.d, T.sub.d') between the beginning of this reference signal (U.sub.dif) and the attainment of a second predetermined rotational position of the rotor;
• d) a calculation component, for influencing the time a stator current serving to drive the motor is switched, according to at least one predetermined rule and, based on the magnitude of the difference in time (T.sub.d, T.sub.d') and on whether the attainment of the second predetermined rotational position of the rotor occurred before or after the beginning of said reference signal;
• and
• e) means for resetting the voltage on said capacitor to an initial value after the changing of said voltage as a function of time is terminated.

An electronically commutated DC motor having

• a control circuit controlling current flowing in said motor and successively executing, in operation, program loops each having substantially the same predetermined duration;
• a loop counter counting said loops approximately beginning at a first rotational position of said rotor and ending substantially at a point in time when said rotor has rotated through a predetermined angle from said first rotational position;
• a comparing step in said loop which continuously compares a count value in said loop counter to a predetermined threshold value;
• and
• an alarm generator, actuatable by said comparing step, which generates an alarm signal when the count value in said loop counter exceed said predetermined threshold value.

A method of monitoring the speed of an electronically commutated DC motor having a stator and a rotor, comprising the following steps:

• a) repeatedly and successively executing, as said rotor is rotating through a predetermined rotational angle range relative to said stator, a program loop of predetermined duration and containing steps controlling said motor;
• b) starting substantially at the beginning of said rotational angle range, and ending substantially at the end thereof, counting the number of said program loops executed, and monitoring continuously the thus-obtained count value obtained as the rotor rotates through said rotational angle range;
• and
• c) when said count value exceeds a predetermined threshold value, generating an alarm signal.