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Stepper motor is an open-loop control element that converts electric pulse signal into angular displacement or linear displacement. In the case of non overload, the speed and stop position of the motor only depend on the frequency and number of pulses of the pulse signal, and are not affected by the load change, that is, add a pulse signal to the motor, and the motor will turn a step angle. The existence of this linear relationship, coupled with the stepper motor has the characteristics of only periodic error and no cumulative error. It makes it very simple to control with stepper motor in the field of speed, position and so on. Although stepper motor has been widely used, stepper motor can not be used under conventional conditions like ordinary DC motor  AC motor. It must be composed of double ring pulse signal and power driving circuit before it can be used in the control system.
Dynamic index and terminology of stepping motor
step angle accuracy
The error between the actual value and the theoretical value of each step angle of the stepping motor. Expressed as a percentage, error / step angle * 100%. The value of different running beats is different. It should be within 5% in four beat operation and 15% in eight beat operation.
Out of step
The number of steps during motor operation is not equal to the number of steps in theory. Call it out of step.
Maladjustment angle
When the rotor tooth axis deviates from the stator tooth axis, the motor operation must have an offset angle. The error caused by the offset angle cannot be solved by subdivision drive.
Maximum no-load starting frequency
The maximum frequency at which the motor can be started directly without load under certain driving form, voltage and rated current.
Maximum no-load operating frequency
The maximum speed frequency of the motor without load under a certain driving form, voltage and rated current. six Operating torque frequency characteristics
The curve of the relationship between output torque and frequency measured by the motor under certain test conditions is called operating torque frequency characteristic, which is the most important of many dynamic curves of the motor and the fundamental basis for motor selection. It also has inertia frequency characteristics, starting frequency characteristics and so on. To increase the average current, increase the driving voltage as much as possible, so that the motor with small inductance and high current can be used.
Motor forward and reverse control
When the power on sequence of motor winding is ab-bc-cd-da or (), it is forward rotation  when the power on sequence is da-ca-bc-ab, it is reverse rotation.
Composition of drive control system
The use and control of stepping motor must be a control system composed of ring pulse, power amplification, etc
Generation of pulse signal
Pulse signal is generally generated by single chip microcomputer or CPU. Generally, the duty cycle of pulse signal is about 0.3-0.4. The higher the motor speed, the greater the duty cycle.
Signal distribution
Two phase four beat, step angle of 1.8 degrees; Two phase eight beat, with a step angle of 0.9 degrees; There are also two working modes of four phase motor. Four phase four beat is ab-bc-cd-da-ab, with a step angle of 1.8 degrees, and four phase eight beat is ab-b-bc-c-cd-d-ab (with a step angle of 0.9 degrees).
Power amplification
Power amplification is the most important part of the drive system. The torque of stepper motor at a certain speed depends on its dynamic average current rather than static current. So far, there are generally the following driving modes: constant voltage, constant voltage series resistance, high and low voltage driving, constant current, fine fraction, etc. The higher the speed of the stepping motor and the larger the force distance, the greater the current of the motor and the higher the voltage of the driving power supply. Subdivision drive
When the step angle of the stepping motor can not meet the use conditions, the subdivision driver can be used to drive the stepping motor. The principle of the subdivision driver is to control the operation of the stepping motor by changing the adjacent-a-b-current to change the included angle of the synthetic magnetic field.
Selection of stepping motor
Stepper motor is composed of three elements: step angle, phase number, static torque and current. Once the three elements are determined, the model of the stepping motor is determined.
Selection of step angle
The step angle of the motor depends on the requirements of load accuracy. The minimum resolution and equivalent of the load are converted to the motor shaft. How many angles should each equivalent motor go, including deceleration, and the step angle of the motor should be equal to or less than this angle. At present, the step angle of stepping motor in the market is generally 0.36 degrees / 0.72 degrees, five phase motor 0.9 degrees / 1.8 degrees, and two and four phase motor 1.5 degrees / 3 degrees.
Selection of static moment
It is difficult to determine the dynamic torque of the stepping motor at once. We often determine the static torque of the motor first. The selection of static torque is based on the working load of the motor, and the load can be divided into inertia load and friction load. Once the static torque is selected, the geometric dimensions of the motor base and length can be determined.
Selection of current
The operating characteristics of motors with the same static torque vary greatly due to different current parameters. The current of the motor can be judged according to the torque frequency characteristic curve, with reference to the driving power supply and driving voltage.
Torque and power conversion
Stepper motors are generally used for speed regulation in a large range, and their power changes. Generally, they are measured only by torque. The conversion between torque and power is as follows;
P= Ω·M
P is the power, in watts; Ω is the angular velocity per second, in radians; N is the speed per minute; M is the moment, in Newton · m; P = 2 π FM / 400 (half step operation, where f is the number of pulses per second, abbreviated as PPS)