The difference between the stepper motor and servo motor

Stepper motor is the electrical pulse signal into angular displacement or line displacement of the stepper motor open-loop control yuan, in the case of the overload, motor speed, stop position depends only on the pulse signal frequency and pulse number, and not affected by load change, when the stepper driver receives a pulse signal, it is driving a stepper motor, set the direction of a fixed Angle, called interval Angle, its rotation is based on the Angle of the fixed step by step. Can be controlled by controlling the pulse number of angular displacement, so as to achieve the purpose of accurate positioning, as well as by controlling the pulse frequency to control motor rotation speed and acceleration, so as to achieve the purpose of high speed. Servo motor is also called the execution, in the automatic control system, is used as actuators, the received electrical signal into angular displacement or angular velocity output of motor shaft. The inside of the servo motor rotor is a permanent magnets, three-phase electric drive control of U/V/W form the electromagnetic field, under the action of rotating rotor in this field, at the same time, motor with encoder feedback signal to drive, drive according to the feedback value compared with the target, adjust the Angle of the rotor rotation. The precision of servo motor is determined by the precision of the encoder ( Line number) 。 That is the function of the servo motor itself has a pulse, it every rotation Angle, send out the corresponding number of pulses, such servo drive and servo motor encoder pulse forming the echo, so it is a closed loop control, step motor is open loop control. Stepping motor and servo motor difference is: 1, control precision is different. Stepping motor phase and shoot, the more its precision is higher, the servo motor to take to bring their own piece of encoder, the more the encoder scale, the higher the precision. 2, control in a different way; One is the open loop control, a closed loop control. 3, low frequency characteristics of different; Stepper motor at low speed is easy to appear low frequency vibration phenomenon, when it is commonly used while working in low-speed damping technology or segmentation technology to overcome the low frequency vibration phenomenon, servo motor running smoothly, even in the low speed also won't appear when the vibration phenomenon. Ac servo system has a resonance suppression function, can cover mechanical rigidity, and the system has the function of frequency resolution ( FFT) , can detect the mechanical resonance point to facilitate system adjustment. 4, different torque frequency characteristics; Stepper motor with higher speed and the decrease of the output torque of ac servo motor as the constant torque output, 5, overload capacity; Stepper motor is generally not has overload capacity and the ac motor has the strong ability of overload. 6, different running performance; Stepper motor control for the open loop control, start frequency is too high or too much load step is easy to lose or locked-rotor phenomenon, stop when high speed impact occurred easily, ac servo drive system for closed-loop control, the drive can be directly to the motor encoder feedback signal sampling, internal position loop and speed loop, general won't appear step motor lose step or overshoot phenomenon, more reliable control performance. 7, the speed response performance; Stepper motor speed accelerate from 0 to work requires hundreds of milliseconds, and better acceleration performance of the ac servo system, generally only a few milliseconds, can be used for quick start-stop control occasions. To sum up, the ac servo system in many performance is better than the stepping motor, but the price is different.