Method for determining a lead torque of an elevator system

A method for determining a lead torque of an elevator system, the elevator system including an elevator shaft, an elevator car movable along the elevator shaft between a first position and a second position, the elevator car being coupled to a counterweight via suspension means, and an electric motor with a traction sheave that drives the suspension means thereby moving the elevator car and the counterweight in the elevator shaft, the method comprising the steps of:

• generating control commands that control the electric motor such that the elevator car performs a first test run, a second test run, a third test run and a fourth test run;
• wherein the elevator car moves from the first position to the second position during each of the first test run and the third test run and the elevator car moves from the second position to the first position during each of the second test run and the fourth test run;
• wherein the elevator car is loaded with a predetermined weight during the third test run and the fourth test run and is not loaded with the weight during the first test run and second test run;
• receiving current measurement data indicating an electric current that flows through the electric motor and is measured by a current measuring device during the movement of the elevator car in each of the test runs, and receiving height measurement data indicating a height of the elevator car relative to the first position and/or second position and measured by a height measuring device in a plurality of successive time steps during the movement of the elevator car in each of the test runs;
• calculating at least one parameter of a calibration function that defines a relationship between the current, the height and the weight, using the current measurement data and the height measurement data received during the test runs, to obtain at least one calibration value;
• calculating a first weight difference representative of a weight difference between a first mass of the elevator system on one side of the traction sheave of the electric motor and a second mass of the elevator system on an opposite side of the traction sheave when the elevator car is in the first position;
• calculating a second weight difference representative of a weight difference between a third mass of the elevator system on the one side of the traction sheave and a fourth mass of the elevator system on the opposite side of the traction sheave when the elevator car is in the second position;
• calculating the first weight difference and the second weight difference using the calibration function and the at least one calibration value;
• and
• determining a lead torque for applying to the electric motor before the elevator car is moved in response to the first weight difference and the second weight difference.