Research on torque-variable control method for stepping motors in service robot arm

Stepping motors are applied to service robots in many cases, unfortunately stepping motors often occur out-of-step situation when it is overload. In order to sense the occurrence of out-of-step without the help from external sensors, its feedback could only induce from its inner structure of the stepping motor. In other words, occurrence of out-of-step cause variable back electromotive force (emf) which cause fluctuation of phase current change. By detecting the change of phase current, the occurrence of out-of-step becomes more observable. Based on the feedback which is the phase current change, a new control system is introduced in this paper, which inserts feedback into a PID regulator to increase the input current and further increase output torque of motor shaft simultaneously. Based on the simulation result in Matlab, the stepping motor is able to make sure the shaft is in its static state even though load torque is larger than normal value. Therefore, service robot arm has much strength to hold heavy things than before.