Robust Over-current Protection & Stall detection techniques for Stepper Motor Drive

Stepper motor is an electromechanical system that rotates in terms of small precise increments without a need to govern the movement. It offers many advantages over traditional DC motor such as higher start-up torque, faster acceleration, wide dynamic range, good speed-stability with fluctuating load, cost effective and easier open loop drive requirements etc. Certain disadvantages also come with stepper motor; to name a few, open loop operation fails to provide information about absolute position or whether motor is responding to input commands in absence any position sensor. In situations where, very high reliable hardware performance and safety are demanded, it is highly recommended to sense the load overcurrent and take necessary safety actions. Also in situation where stepper motor stalls due to any unforeseen problems, it is necessary to detect and take safety actions, otherwise it may lead to motor overheating and eventually thermal run away. Understanding such situations, this paper describes innovative and robust techniques for Sensorless stall detection along with over-current protection of drive electronics system using minimal hardware. Stepper motor here is driven in Pulse-Width-Modulation (PWM) based full-step and microstepping mode of control. Back Electromagnetic Force (BEMF) is sensed to detect motor stalling. Over-current detection and protection logic uses the same PWM current control loop to detect current shoot-through condition in motor drive without addition of extra circuitry. This paper presents design, mathematical simulation, hardware implementation, testing and analysis of experimental results for these hardware safety techniques.