Method and a device for detecting abnormal changes in play in a transmission unit of a movable mechanical unit

A device for detecting abnormal changes in play in a transmission unit configured to transfer rotational movements of a motor, having a speed of rotation that depends on a torque reference signal, to a movable mechanical unit, wherein the device comprises:

• a first storage medium for storing the torque reference signal value for the motor at least in a time interval during which the motor is running at a steady state rotation speed,
• a computing unit configured,
• to retrieve measured rotation speed values of the motor during said time interval,
• to identify the steady state rotation speed of the retrieved rotation speed values,
• to calculate a power spectrum of the torque reference signal,
• to calculate the energy generated around the second harmonic of the identified steady state rotation speed in a selected frequency band around a peak value of the second harmonic in the calculated power spectrum,
• to compare the calculated energy with at least one limit value, and
• based thereon, to detect abnormal changes in the play.

A computer program product stored on a non-transitory computer readable medium for detecting abnormal changes in play in a transmission unit configured to transfer rotational movements of a motor, having a speed of rotation that depends on a torque reference signal, to a movable mechanical unit, wherein the computer program product is directly loadable into the internal memory of a computer, comprising software to perform the steps:

• a. saving the torque reference signal values for the motor at least in a time interval during which the motor is running at a steady state rotation speed,
• b. retrieving measured rotation speed values of the motor during said time interval,
• c. identifying the steady state rotation speed of the retrieved rotation speed values,
• d. calculating a frequency spectrum of the torque reference signal,
• e. calculating the energy generated around the second harmonic of the identified steady state rotation speed in a selected frequency band around a peak value of the second harmonic in the calculated frequency spectrum,
• comparing the calculated energy with at least one limit value, and
• based thereon detecting abnormal changes in the play.