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Step motor characteristics and how to choose?
Date：May 17th,2023
With the increasing importance of the control motor, the use of the control motor also increases year by year. Stepper motor is a kind of control motor, without using the feedback loop, it can conduct the speed control and positioning control, namely the so-called motor open loop control.
Its application is mainly based on OA machines and FA machines with strong office business ability as the core, and is widely used in medical devices, measuring instruments, automobiles, game consoles, etc. In terms of quantity, 0A machine applications account for about 75% of the total stepper motor use.
1. Principle of the stepping motor
Stepper motor is a motor that uses the principle of electromagnet to convert the pulse signal into line displacement or angular displacement. With each electric pulse, the motor rotates at an Angle, drive the machinery to move a short distance.
2. classify
Motor has various classification, such as AC drive and AC drive for voltage classification, and synchronous motor and assynchronous motor.
The stepper motor is a synchronous motor driven by DC, but it cannot be driven directly by DC or AC power supply. It needs to be equipped with a driver to use it. So the operation of the stepping motor requires the drive circuit. This point is the same as the brushless DC motor, the brushless DC motor to use the drive circuit, the drive circuit will be the motor stator and the DC power supply connected to work together.
3. Stepper motor characteristics
The basic characteristics of the stepping motor include motor static characteristics, continuous motion characteristics (dynamic characteristics), motor starting characteristics and motor braking characteristics (transient characteristics). The following are introduced respectively:
1. Static torque characteristics
When the coil of the stepping motor is directly connected, the relationship between the electromagnetic torque with the load rotor (the recovery electromagnetic torque generated by the load torque balance is called static torque or static torque) and the rotor power angle is called the Angle-static torque characteristic, which is the static characteristic of the motor.
Because the rotor is a permanent magnet, the resulting magnetic air gap is sinusoidal distribution, so theoretically the static torque curve is sinusoidal wave. This Angle-static torque characteristic is an important indicator of the ability of the stepping motor to produce electromagnetic torque. The greater the maximum torque, the better, and the closer the torque waveform is to the sine, the better. In fact, there is a slot torque under the magnetic pole, which distorts the synthetic torque. For example, the groove torque of the two-phase motor is 4 times the harmonic period of the stationary torque, and added to the stationary torque of the sine, the torque shown in the above figure is:
TL=TMsin[(θL/θM)π/2]
The TL and TM each represent the load torque and the maximum static torque (or hold torque), and the corresponding power angles are θ L and θ M. The change of this displacement angle determines the position accuracy of the stepper motor. According to the above equation:
θL=(2θM/π)arcsin(TL/TM)
The step Angle of PM permanent magnet stepping motor and HB hybrid stepping motor θ s was mentioned in the previous course: θ s=180 / PNr, the Angle is changed to mechanical Angle (radian), then the following formula:
θs=π/(2Nr)
The upper formula Nr is the number of rotor teeth or the polar logarithm, so the two-phase motor θ M= θ s.
2. Dynamic torque characteristics
Dynamic torque characteristics include drive pulse frequency-torque characteristics and drive pulse frequency-inertia characteristics.
1) Pulse frequency-torque characteristics
Pulse frequency-torque characteristic is an important choice of stepping motor
Its application is mainly based on OA machines and FA machines with strong office business ability as the core, and is widely used in medical devices, measuring instruments, automobiles, game consoles, etc. In terms of quantity, 0A machine applications account for about 75% of the total stepper motor use.
1. Principle of the stepping motor
Stepper motor is a motor that uses the principle of electromagnet to convert the pulse signal into line displacement or angular displacement. With each electric pulse, the motor rotates at an Angle, drive the machinery to move a short distance.
2. classify
Motor has various classification, such as AC drive and AC drive for voltage classification, and synchronous motor and assynchronous motor.
The stepper motor is a synchronous motor driven by DC, but it cannot be driven directly by DC or AC power supply. It needs to be equipped with a driver to use it. So the operation of the stepping motor requires the drive circuit. This point is the same as the brushless DC motor, the brushless DC motor to use the drive circuit, the drive circuit will be the motor stator and the DC power supply connected to work together.
3. Stepper motor characteristics
The basic characteristics of the stepping motor include motor static characteristics, continuous motion characteristics (dynamic characteristics), motor starting characteristics and motor braking characteristics (transient characteristics). The following are introduced respectively:
1. Static torque characteristics
When the coil of the stepping motor is directly connected, the relationship between the electromagnetic torque with the load rotor (the recovery electromagnetic torque generated by the load torque balance is called static torque or static torque) and the rotor power angle is called the Angle-static torque characteristic, which is the static characteristic of the motor.
Because the rotor is a permanent magnet, the resulting magnetic air gap is sinusoidal distribution, so theoretically the static torque curve is sinusoidal wave. This Angle-static torque characteristic is an important indicator of the ability of the stepping motor to produce electromagnetic torque. The greater the maximum torque, the better, and the closer the torque waveform is to the sine, the better. In fact, there is a slot torque under the magnetic pole, which distorts the synthetic torque. For example, the groove torque of the two-phase motor is 4 times the harmonic period of the stationary torque, and added to the stationary torque of the sine, the torque shown in the above figure is:
TL=TMsin[(θL/θM)π/2]
The TL and TM each represent the load torque and the maximum static torque (or hold torque), and the corresponding power angles are θ L and θ M. The change of this displacement angle determines the position accuracy of the stepper motor. According to the above equation:
θL=(2θM/π)arcsin(TL/TM)
The step Angle of PM permanent magnet stepping motor and HB hybrid stepping motor θ s was mentioned in the previous course: θ s=180 / PNr, the Angle is changed to mechanical Angle (radian), then the following formula:
θs=π/(2Nr)
The upper formula Nr is the number of rotor teeth or the polar logarithm, so the two-phase motor θ M= θ s.
2. Dynamic torque characteristics
Dynamic torque characteristics include drive pulse frequency-torque characteristics and drive pulse frequency-inertia characteristics.
1) Pulse frequency-torque characteristics
Pulse frequency-torque characteristic is an important choice of stepping motor