Patent ID: 7777442

Claim:
A method of controlling the speed of an electric motor powered by a triac to maintain a preset speed, by varying the electrical angle at which the triac is triggered, comprising the steps of: producing a signal related to the first derivative of the motor speed; producing a signal related to the difference in value between the motor current speed and the preset speed (Error P); and producing a control signal based on said first derivative related signal and said Error P related signal to adjust the triac electrical triggering angle to operate the motor at the preset speed, wherein: the step of producing said first derivative related signal further comprises the steps of measuring the motor speed at different times and calculating the first derivative of the measured motor speed, determining a yield value (Yield D) of the value of the first derivative from a numerical range of values, and producing a band (Band D) value as the product of the value of said calculated first derivative and said Yield D value; the step of producing said signal related to said Error P value further comprises the steps of: determining a yield value (Yield P) of the Error P value from a numerical range of values, and producing a band (Band P) value as the product of the value of said Error P signal and said Yield P value; and the step of producing said control signal further comprises the steps of: producing a signal of the sum of said Band D and said Band P values (Total Error), and converting said Total Error signal into a signal which corresponds to the error of the triac electrical triggering angle needed to achieve the motor preset speed.