Stepper motor parameters

Motor inherent step angle: It indicates the angle that the motor rotates every time the control system sends a step pulse signal.

The number of phases of a stepper motor refers to the number of coil groups inside the motor. Currently, two-phase, three-phase, four-phase, and five-phase stepper motors are commonly used. The step angles of motors with different phases are also different. Generally, the step angles of two-phase motors are 0.9°/1.8°, three-phase motors are 0.75°/1.5°, and five-phase motors are 0.36°/0.72°.

Holding torque: refers to the torque of the stator locking the rotor when the stepper motor is powered but not rotating. It is one of the most important parameters of the stepper motor. Usually, the torque of the stepper motor at low speed is close to the holding torque.

Phase number: The number of pairs of exciting coils that generate N and S magnetic fields of different poles refers to the number of coil groups inside the motor. Currently, two-phase, three-phase, four-phase, and five-phase stepper motors are commonly used. The step angle of the motor is different for different phases. Generally, the step angle of a two-phase motor is 0.9°/1.8°, that of a three-phase is 0.75°/1.5°, and that of a five-phase is 0.36°/0.72°. When there is no subdivision driver, users mainly rely on selecting stepper motors with different phases to meet their step angle requirements. If a subdivision driver is used, the "number of phases" will become meaningless. Users only need to change the number of subdivisions on the driver to change the step angle. Currently, the most widely used are two-phase and four-phase. Four-phase motors are generally used as two-phase, and the cost of five-phase is higher.

Beat number: The number of pulses or conductive states required to complete a periodic change of the magnetic field is represented by n, or the number of pulses required for the motor to rotate through a pitch angle. Taking a four-phase motor as an example, there are four-phase four-beat operation modes, namely AB-BC-CD-DA-AB, and four-phase eight-beat operation modes, namely A-AB-B-BC-C-CD-D-DA-A.

Intrinsic step angle: Corresponding to a pulse signal, the angular displacement of the motor rotor is represented by θ. θ=360 degrees (rotor teeth number J*operation beat number), taking a conventional two-phase or four-phase motor with 50 rotor teeth as an example. When running with four beats, the step angle is θ=360 degrees/(50*4)=1.8 degrees (commonly known as full step), and when running with eight beats, the step angle is θ=360 degrees/(50*8)=0.9 degrees (commonly known as half step). This step angle can be called the 'motor inherent step angle', which is not necessarily the true step angle when the motor is actually working. The true step angle is related to the driver.

Detent Torque: The locking torque of the motor rotor itself when the motor is not powered (caused by the harmonics of the magnetic field tooth profile and mechanical errors). There is no unified translation method for DETENT TORQUE in China, which can easily lead to misunderstandings. Since the rotor of the reactive stepper motor is not made of permanent magnet material, it does not have DETENT TORQUE.

Maximum static torque: also called holding torque (HOLDING TORQUE), the locking torque of the motor shaft when the motor is under rated static electrical action (power on), that is, the torque of the stator locking the rotor. This torque is a standard for measuring the volume (geometric dimensions) of the motor and has nothing to do with the drive voltage and drive power supply. Usually, the torque of the stepper motor at low speed is close to the holding torque. Since the output torque of the stepper motor continues to decay with the increase of speed, and the output power also changes with the increase of speed, the holding torque has become one of the most important parameters for measuring stepper motors. For example, when people say a 2N.m stepper motor, it means a stepper motor with a holding torque of 2N.m without special instructions.
Although the static torque is proportional to the electromagnetic excitation ampere-turns and is related to the air gap between the stator and the rotor, it is not advisable to excessively reduce the air gap and increase the excitation ampere-turns to increase the static torque, which will cause heating and mechanical noise of the motor.
Selection of maximum static torque:
It is difficult to determine the dynamic torque of a stepper motor at once, so we often determine the static torque of the motor first. The basis for selecting the static torque is the load of the motor, and the load can be divided into two types: inertia load and friction load. Single inertia load and single friction load do not exist. When starting directly (usually at low speed), both loads must be considered. When starting at an accelerated speed, the inertia load is mainly considered. When running at a constant speed, only the friction load needs to be considered. In general, the static torque should be within 2-3 times the friction load. Once the static torque is selected, the motor base and length can be determined (geometric dimensions).

Application of stepper motors
The characteristics of stepper motors are mainly attributed to three aspects:
good overload resistance, used in situations with strict requirements on speed and position;
easy control, stepper motors rotate in "steps", digital characteristics are relatively obvious, which brings great convenience to computer control.
The whole machine structure is simple, and the structure becomes simple and compact.