Patent ID: 8169169

Claim:
A door operator for controlling operation of a door, the door operator having a motor to open the door against a spring force, said door operator further comprising: a door position sensor for transmitting a signal indicative of door position; and a controller for: controlling a motor current to generate a predetermined motor force to open the door to a predetermined angle; receiving the signal from the door position sensor and determining a door position and a door speed based on the signal; measuring the time for the door to reach the predetermined angle from a closed position; measuring the current to hold the door at the predetermined angle; converting the measured current to an equivalent force of the motor acting on the spring, which represents the spring force; determining a first torque value acting on the door based on the spring force; determining a second torque value acting on the door based on the predetermined motor force to open the door to the predetermined angle; subtracting the first torque value from the second torque value to determine a net torque acting on the door; and calculating a door moment of inertia based on the net torque and the time for the door to reach the predetermined angle from the closed position.