Ripple count circuit
A motor control system includes a variable voltage supply in signal communication with a direct current (DC) motor. The DC motor includes a rotor induced to rotate in response to a drive current generated by a variable supply voltage delivered by the voltage supply. The rotation of the rotor generates a mechanical force that drives a component. A ripple count circuit is configured to filter the drive current based on a rotational speed (ω) of the rotor, and to generate a pulsed output signal indicative of the rotational speed (ω) of the rotor and a rotational position (θ) of the rotor.
1. A method of determining a rotor speed of a direct current (DC) motor, the method comprising:
generating a variable supply voltage;
applying the variable supply voltage to the DC motor to induce a drive current, and rotating a rotor included in the DC motor based on the drive current;
generating a mechanical force in response to rotating the rotor to drive a component;
filtering the drive current to generate a filtered drive current; and
based on the filtered drive current, generating a pulsed output signal indicative of a rotational speed (ω) of the rotor and a rotational position (θ) of the rotor,
wherein the drive current is filtered based on the rotational speed (ω) of the rotor indicated by the pulsed output signal, and
wherein filtering the drive current comprises:
delivering the drive current to a bandwidth filter having variable center frequency (f O ) that is actively set according to the rotational speed (ω) of the rotor; and
outputting the filtered drive current from the bandwidth filter according to the variable center frequency (f O ).
2. The method of claim 1 , wherein generating the pulsed output signal comprises:
comparing the filtered drive current to a reference voltage potential;
outputting the pulsed output signal having a first output voltage level when a voltage level of the filtered drive current is greater than or equal to the reference voltage potential; and
outputting the pulsed output signal having a second output voltage level when a voltage level of the filtered drive current is less than the reference voltage potential.
3. The method of claim 1 , wherein filtering the drive current comprises performing, by the bandwidth filter, a first filtering operation on the drive current, the first filtering operating including a bandwidth filtering operation that filters the drive current based on a varying center frequency that is actively set based on the rotational speed (ω) of the rotor.
4. The method of claim 3 , wherein filtering the drive current further comprises performing, by the bandwidth filter, a second filtering operation following the first filter operation to eliminate harmonics from the filtered drive current.
5. The method of claim 4 , wherein the second filtering operation includes performing a low pass filtering operation based on a frequency cutoff that is actively set according to the rotational speed (ω) of the rotor.
6. The method of claim 1 , further comprising actively adjusting a voltage level of the variable supply voltage based on at least one of the rotational speed (ω) and the rotational position (θ) indicated by the pulsed output signal.