Patent ID: 7178412

Claim:
A machine comprising: a rotatable component; and a control system, the control system comprising: an encoder to generate a signal corresponding to a rotational movement of the rotatable component and coupled to the rotatable component; speed sensing circuitry coupled to the encoder to generate a signal corresponding to a sensed speed of the rotatable component; torque control circuitry to generate a control signal to control a torque of the rotatable component; and encoder failure detection circuitry to monitor the signal corresponding to a rotational movement of the rotatable component and the control signal to control a torque of the rotatable component, wherein the encoder failure detection circuitry is configured to generate a signal corresponding to a failure of the encoder if: the signal corresponding to a sensed speed is below a first threshold value; the signal to control a torque of the rotatable component continuously exceeds a second threshold value for a selected period of time; and the signal corresponding to a rotational movement of the rotatable component does not indicate a movement during the selected period of time.