Holding Torque And Positioning Torque Of Stepping Motor

- Nov 30, 2018-

Holding torque and positioning torque of stepping motor

Maintaining the torque refers to the maximum torque that the motor can output when the motor's phase windings pass the rated current and is in the static lock state. It is one of the most important parameters when selecting a motor.

The positioning torque refers to the torque generated by the permanent magnet material on the rotor of the hybrid motor when the motor windings of the motor are not energized and are in an open state. Generally, the positioning torque is much smaller than the holding torque. Whether or not there is a positioning torque is an important sign that a hybrid stepping motor is different from a reactive stepping motor.

As an actuator, stepper motor is one of the key products of mechatronics and is widely used in various automation control systems. With the development of microelectronics and computer technology, the demand for stepper motors is increasing day by day, and it has applications in various national economic fields.

A stepper motor is an actuator that converts electrical pulses into angular displacement. When the stepper driver receives a pulse signal, it drives the stepper motor to rotate a fixed angle (called the "step angle") in a set direction, and its rotation is step by step at a fixed angle. The angular displacement can be controlled by controlling the number of pulses to achieve the purpose of accurate positioning. At the same time, the speed and acceleration of the motor rotation can be controlled by controlling the pulse frequency, thereby achieving the purpose of speed regulation. The stepping motor can be used as a special motor for control, and it is widely used in various open-loop control because it has no accumulation error (100% accuracy).

More commonly used stepper motors include reactive stepper motors (VR), permanent magnet stepper motors (PM), hybrid stepper motors (HB), and single-phase stepper motors.

Permanent magnet stepping motor is generally two-phase, torque and volume are small, the step angle is generally 7.5 degrees or 15 degrees; reactive stepping motor is generally three-phase, can achieve large torque output, step angle is generally It is 1.5 degrees, but the noise and vibration are very large. The rotor of the reactive stepping motor is made of soft magnetic material, and the multi-phase excitation winding is arranged on the stator, and the torque is generated by the change of the magnetic permeability.

Hybrid stepper motors are a combination of permanent magnet and reactive. It is divided into two phases and five phases: the two-phase step angle is generally 1.8 degrees and the five-phase step angle is generally 0.72 degrees. This stepper motor is the most widely used and is the stepper motor selected for this subdivision drive scheme. Some basic parameters of the stepper motor;

Inherent step angle of the motor:

It represents the angle at which the motor rotates each time the control system sends a step pulse signal. The motor is given a step angle value when it leaves the factory. For example, the 86BYG250A motor gives a value of 0.9°/1.8° (0.9° for half-step operation and 1.8° for full-step operation). This step angle It can be called 'the inherent step angle of the motor', it is not necessarily the true step angle of the actual working of the motor, and the true step angle is related to the drive. The number of phases of the stepper motor:

It refers to the number of coil groups inside the motor. Currently, two-phase, three-phase, four-phase, five-phase stepping motors are commonly used. The number of phases of the motor is different, and the step angle is also different. Generally, the step angle of the two-phase motor is 0.9°/1.8°, the three-phase is 0.75°/1.5°, and the five-phase is 0.36°/0.72°. When there is no subdivision driver, the user mainly chooses the stepping motor with different phase numbers to meet the requirements of the step angle. If you use a subdivision drive, the 'phase number' will become meaningless, and the user can change the step angle by simply changing the number of subdivisions on the drive.

Hold torque (HOLDINGTORQUE):

It refers to the moment that the stator locks the rotor when the stepper motor is energized but does not rotate. It is one of the most important parameters of a stepper motor. Usually, the torque of the stepper motor at low speed is close to the holding torque. Since the output torque of the stepping motor is continuously attenuated as the speed increases, the output power also changes with the increase of the speed, so the holding torque becomes one of the most important parameters for measuring the stepping motor. For example, when people say that a 2N.m stepper motor, unless otherwise specified, is a stepper motor that maintains a torque of 2N.m.

Positioning torque (DETENTTORQUE):

It refers to the moment that the stator locks the rotor when the stepper motor is not energized. DETENTTORQUE does not have a unified translation method in China, which is easy to misunderstand. Since the rotor of the reactive stepping motor is not a permanent magnet material, it does not have DETENTTORQUE. Some features of the stepper motor:

1. The accuracy of a general stepper motor is 3-5% of the step angle and does not accumulate. 2. The maximum temperature allowed by the stepper motor appearance.

If the temperature of the stepper motor is too high, the magnetic material of the motor will be demagnetized firstly, resulting in torque drop and even out of step. Therefore, the maximum allowable temperature of the motor surface should depend on the demagnetization point of the magnetic material of different motors; in general, the demagnetization of the magnetic material The points are all above 130 degrees Celsius, and some even up to 200 degrees Celsius, so the external temperature of the stepper motor is completely normal at 80-90 degrees Celsius.

3. The torque of the stepper motor will decrease as the speed increases.

When the stepper motor rotates, the inductance of each phase winding of the motor will form a back electromotive force; the higher the frequency, the larger the back electromotive force. Under its action, the motor decreases with increasing frequency (or speed), resulting in a drop in torque.

4. The stepper motor can run normally at low speed, but if it is higher than a certain speed, it cannot be started, accompanied by howling. The stepping motor has a technical parameter: the no-load starting frequency, that is, the pulse frequency that the stepping motor can start normally under no-load conditions. If the pulse frequency is higher than this value, the motor cannot start normally, and lost or blocked may occur. In the case of load, the starting frequency should be lower. If the motor is to be rotated at a high speed, the pulse frequency should have an acceleration process, that is, the starting frequency is low, and then rise to a desired high frequency (the motor speed is increased from a low speed to a high speed) at a certain acceleration. With its remarkable features, stepper motors play a major role in the digital manufacturing era. With the development of different digital technologies and the improvement of the technology of stepping motors, stepping motors will be applied in more fields.

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