Method for maintenance of a transportation device propelled by an electric motor, wherein an incremental encoder senses motion of a moving part of or a part moved by said electric motor, wherein a motor model is used in control of said electric motor, wherein said method comprises: - acquiring a pulses-per-rotation configuration value PPRconf, representing a number of pulses which should be provided by the incremental encoder per one rotation of the electric motor in normal operation; - characterized in deriving a pulses-per-rotation estimation value PPRest representing a number of pulses per one rotation of the electric motor, based on motor model information of an electrical motor control, wherein the deriving a pulses-per-rotation estimation value PPRest comprises the steps: - measuring a stator current (i) of a stator winding of said electric motor; - estimating or measuring a stator voltage of a stator winding of said electric motor; - estimating a magnetic pole position of the magnetic pole of the rotor of said electric motor with the motor model, based on said measured stator current (i) and determined stator voltage; - counting output pulses of the incremental encoder, to obtain an encoder pulse count (n); - determining a position error (Δθ) of a rotor of said electric motor, based on said estimated magnetic pole position and counted encoder pulses; - correcting said counted encoder pulses by means of said determined position error (Δθ), to obtain a corrected encoder pulse count; and - comparing said corrected encoder pulse count with the pulses-per-rotation configuration value PPRconf; - determining a pulses-per-rotation error value PPRerr representing a deviation of the pulses-per-rotation estimation value PPRest from the pulses-per-rotation configuration value PPRconf, based on the relation: PPRerr = PPRest − PPRconf or PPRconf − PPRest or PPRest / PPRconf or PPRconf / PPRest; and - utilizing the pulses-per-rotation error value PPRerr for establishing a maintenance information indicating that a maintenance should be done on the transportation device. - acquiring a pulses-per-rotation configuration value PPRconf, representing a number of pulses which should be provided by the incremental encoder per one rotation of the electric motor in normal operation; - characterized in deriving a pulses-per-rotation estimation value PPRest representing a number of pulses per one rotation of the electric motor, based on motor model information of an electrical motor control, wherein the deriving a pulses-per-rotation estimation value PPRest comprises the steps: - measuring a stator current (i) of a stator winding of said electric motor; - estimating or measuring a stator voltage of a stator winding of said electric motor; - estimating a magnetic pole position of the magnetic pole of the rotor of said electric motor with the motor model, based on said measured stator current (i) and determined stator voltage; - counting output pulses of the incremental encoder, to obtain an encoder pulse count (n); - determining a position error (Δθ) of a rotor of said electric motor, based on said estimated magnetic pole position and counted encoder pulses; - correcting said counted encoder pulses by means of said determined position error (Δθ), to obtain a corrected encoder pulse count; and - comparing said corrected encoder pulse count with the pulses-per-rotation configuration value PPRconf; - measuring a stator current (i) of a stator winding of said electric motor; - estimating or measuring a stator voltage of a stator winding of said electric motor; - estimating a magnetic pole position of the magnetic pole of the rotor of said electric motor with the motor model, based on said measured stator current (i) and determined stator voltage; - counting output pulses of the incremental encoder, to obtain an encoder pulse count (n); - determining a position error (Δθ) of a rotor of said electric motor, based on said estimated magnetic pole position and counted encoder pulses; - correcting said counted encoder pulses by means of said determined position error (Δθ), to obtain a corrected encoder pulse count; and - comparing said corrected encoder pulse count with the pulses-per-rotation configuration value PPRconf; - determining a pulses-per-rotation error value PPRerr representing a deviation of the pulses-per-rotation estimation value PPRest from the pulses-per-rotation configuration value PPRconf, based on the relation: PPRerr = PPRest − PPRconf or PPRconf − PPRest or PPRest / PPRconf or PPRconf / PPRest; and - utilizing the pulses-per-rotation error value PPRerr for establishing a maintenance information indicating that a maintenance should be done on the transportation device.