Patent ID: 7622881

Claim:
A method for estimating inertia of an electric motor that drives a load wherein the load has a limited range of load travel, the method comprising the steps of: identifying an intermediate position along the range of load travel that is separated from a first end of the range of load travel; receiving a sensor signal from a sensor attached to the electric motor; with the load separated from a first end of the range of load travel, increasing a velocity of the electric motor from a first velocity as the load travels toward the first end of the range of load travel; identifying when the load has reached the intermediate position; identifying the motor velocity at the intermediate position as a second velocity; in response to the sensor signal, detecting a first rate of velocity change from the first velocity to the second velocity; acquiring a plurality of torque samples while the electric motor is changing velocity, each torque sample representing an amount of torque generated by the electric motor; calculating a first torque average by averaging the plurality of torque samples; and deriving an inertia value as a function of the first rate of velocity change and the first average amount of torque.