Stepper motor is an open-loop control component that converts electric pulse signal into angular displacement or linear displacement. In the case of non-overload, the motor speed, stop position only depends on the pulse signal frequency and pulse number, and is not affected by the load change, that is, to add a pulse signal to the motor, the motor will turn a step Angle. The existence of this linear relationship, coupled with the stepper motor only periodic error and no cumulative error and so on. It makes it very simple to use stepper motor to control speed, position and other control areas.
1.Stepper motor features
< 1 > the rotation Angle is proportional to the input pulse, so the requirements of high precise Angle and high precision positioning can be achieved by using the open loop control.
< 2 > good start, stop, positive and negative response, easy control.
< 3 > each step of the Angle error is small, and there is no cumulative error.
< 4 > within the controlled range, the speed of rotation is proportional to the frequency of the pulse, so the range of transmission is very wide.
< 5 > at rest, the stepper motor has a high holding torque to stay in the stop position, without the need to use the brake so that it does not rotate freely.
< 6 > has very high RPM.
< 7 > high reliability, no maintenance, low price of the whole system.
< 8 > easy to lose step at high speed
< 9 > tends to produce vibration or resonance phenomenon at a certain frequency
2.Terminology for stepper motors
* Phase number: the logarithm of the excitation coils that generate different magnetic fields for poles N and S. M is commonly used.
* Number of steps: The number of pulses required to complete the periodic change of a magnetic field or the conductive state is represented by N, or the number of pulses required for the motor to rotate a tooth pitch Angle. Take the four-phase motor for example, there is a four-phase four-step execution mode, namely AB-BC-CD-DA-AB, four-phase eight-step execution mode, namely A-AB-B-BC-C-CD-D-DA-A.
* Step Angle: corresponding to a pulse signal, the angular displacement of the motor rotor is represented by. =360 degrees (number of rotor teeth J* number of executive steps). Take conventional two-phase and four-phase motor with rotor teeth as an example of a 50-tooth motor. For the four-step execution, the step Angle is =360 degrees /(50*4)=1.8 degrees (commonly known as the whole step), while for the eight-step execution, the step Angle is =360 degrees /(50*8)=0.9 degrees (commonly known as half step).
* Positioning torque: when the motor is not energized, the locking torque of the motor rotor itself (caused by harmonics of the tooth shape of the magnetic field and mechanical errors).
* Static torque: the locking moment of the motor shaft when the motor is not rotating under rated static electric action. This torque is the standard to measure the volume (geometric size) of the motor and is independent of the driving voltage and power supply. Although the static torque is proportional to the number of electromagnetic excitation ampere-turns and is related to the air gap between the fixed-gear rotor, it is not advisable to excessively reduce the air gap and increase the excitation ampere-turns to improve the static torque, which will cause the motor heating and mechanical noise.
Post time: Dec-02-2020