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1. Selected by the type of PM, VR and HB
According to the structure of the rotor, the stepper motor is divided into the PM type of the stator and the permanent magnet oxygen body consists of the plate gold claw pole and the HB type consists of a rotor consisting of two magnets plus a magnet. Their respective characteristics are shown as shown in the table 2.
When stepping motor is selected, the type of stepper motor should be selected first. At this time as the table 2 shows, four factors like step angle , torque, time constant,and price should be considered. In order to judge which step motor is suitable.
When choosing the stepper motor, the precision of position control, the range of use speed, the load transmission mode (spring load, friction load, gear load, belt drive, spiral transmission), noise and vibration, ambient temperature, environment (dust, oil, humidity) are also considered.
For example, the PM type is not like the HB type ball bearing, but the metal sliding bearing, if the elastic load is applied, using the belt to transfer the load or using the ball screw for torque transmission. The allowable value of the radial load or the thrust load of the metal sliding bearing can be very much, and the use temperature range of the PM type should be paid attention to. VR stepper motor is used as a servo motor, and closed loop control is used when it is used, so VR stepping motor is seldom used. The reason is that its price is close to HB type stepper motor with resolution of HB 1/2 and it is not as efficient as permanent magnet motor, and its transient characteristic is poor. Type HB has high torque and high resolution. It is widely used for location or low speed operation, but it is prone to vibration or noise problems.
2. Selection of phase number of step motor
When selecting stepper motors ,the advantages and disadvantages of the motors should be considered at first, below will introduce the advantages and disadvantages of different phases of motors.1) Two phase PM type stepper motor
① Cheap. Generally it is 1/2 cheaper than the equal size HP type motors.
② Compared with the HB type, the air gap is large, the claw pole structure and the step angle are large, that is, at the same speed, the number of phase switching is low and the noise is low.
① Because of the low resolution (larger angle of 7.5 degrees), the position error is worse than that of HB, especially when the 1 phase excitation is worse. The position accuracy of half step is generally not good. PM type position location is not 2 phase excitation, but it is generally difficult to achieve satisfactory position accuracy. The torque ripple in the low speed range (below 200rpm) is large.
② Because the air gap is large, the roots of the claw pole are easy to produce magnetic saturation, resulting in small output torque.
③ The bearing adopts metal sliding bearing, which has short life.
④ The rotor usually uses a ferrite magnet with poor temperature characteristics. If used for a long time, the torque drop is larger than that of the HB type.
2) Two phase HB type stepper motor
① High resolution (usually more than 1.8 degrees of step angle) is widely used.
② Big torque
③Compared with multi-phase HB stepper motor, the power consumption of driving power is much, but the price is cheap.Disadvantages
① Especially at low speed, the vibration is large, and resonance near 60rpm is easy.
② At high speed, the noise is great.
③ Compared with multiphase HB, the torque ripple in half step is large (1:1.14).
④ Compared with multiphase motor, the synchronous motor with phase synchronous angle has large impedance and small torque at high speed.
3) Three phase HB type stepper motor
① The resolution is 1.5 times that of a two-phase motor and can be used for high-precision location.
② The number of main poles of the stator is 6, the flux of the chain is large, and the torque synthesis efficiency of the two phase excitation is better than that of the two-phase motor, and the torque is higher.
③ Y wiring or delta connection, 3 terminals and 6 power tubes, less than 8 power transistors of two phase motors.
④ Because of the three phase structure, the three harmonic of excitation current is canceled, and vibration and noise are smaller than two phase motors.
⑤ The cogging torque is changed from the 4 harmonic of the two-phase motor to the 6 harmonic of the three-phase motor, and the cogging torque is smaller than that of the two-phase motor.
If it is the 12 main pole, it is more complicated than the 8 main pole structure of the two phase motor.
4）Five phase HB type stepper motor
① The resolution is higher than that of the three-phase motor, and is suitable for high precision requirements.
② In the HB step motor with the same step angle, the torque in the high speed running region is large.
The number of the main poles of the electronic stator is 10 poles, and the power tube of the drive circuit is also 10. The structure of the motor and the driver is complex and the cost is high. It is more suitable for the FA situation than the OA.
5）Three phase RM type stepper motor
① The rotor has no magnetism
② Low vibration and low noise.
③ The position positioning accuracy of the subdivision step is high.
④ High speed torque is large when rotating at high speed.
⑤ The same as the three-phase HB type motor, it can drive Y or delta drive, and the power circuit of the driving circuit is 6.
① The resolution is lower than the HB type
② The cost of the rotor is higher than that of the HB type.
6) Three phase PM type stepper motor
① The resolution is 1.5 times more than the two phase PM motor.
② Vibration and noise are smaller than two phase PM motor or two-phase HB motor.
③ The high speed torque is larger than the two phase PM motor.
④ It is cheaper than HB type
⑤ The advantages of three-phase motors are that they are driven by only 6 power transistors.
The structure of the two phase PM motor is complex.