Permanent Magnet Stepper Motors
Permanent magnet stepper motors use a permanent magnet (PM) in the rotor and operate on the attraction or repulsion between the rotor PM and the stator electromagnets. The step angle for permanent magnet stepping motors is usually 3.75 degrees, 7.5 degrees, 15 degrees, or 18 degrees, depending on the model. They are generally two-phase, have low torque and volume, and have a small step angle. MOONS' PM stepper motors are widely applied in many innovative applications, including computer equipment, photographic systems, optoelectronic devices, valve control, ATM equipment, CNC machine, automatic winding machines, electronic clocks, and medical equipment.
What is a Permanent Magnet Stepper Motor?
The PM motor is an inner rotor type motor, and the outer surface of the cylindrical rotor is evenly distributed with N and S poles.What is a Permanent Magnet Stepper Motor?
Structure
Operating Principles
Operating Principles In response to each individual control pulse and direction signal, the drive applies power to the motor windings to cause the rotor to take a step forward, a step in reverse, or hold in position. For example, in a 7.5 degree two phase step motor: When both phases are energized with DC current, the motor will stop rotating and hold in position. The maximum torque the motor can hold in place with rated DC current, is the rated holding torque. If the current in one phase is reversed, the motor will move 1 step (7.5 degrees) in a known direction. If the current in the other phase had been reversed, the motor would move 1 step (7.5 degrees) in the other direction. As current is reversed in each phase in sequence, the motor continues to step in the desired direction. These steps are very accurate. For a 7.5 degree step motor, there are exactly 48 steps in one revolution. Two phase stepping motors are furnished with two types of windings: bipolar or unipolar. In a bipolar motor there is one winding on each phase. The motor moves in steps as the current in each winding is reversed. This requires a drive with eight electronic switches. In a unipolar motor there are two windings on each phase. The two windings on each phase are connected in opposite directions. Phase current is reversed by turning on alternate windings on the same phase. This requires a drive with only four electronic switches. Bipolar operation typically provides 40% more holding torque than unipolar, because 100% of the winding is energized in the bipolar arrangement. Speed-Torque Characteristics The dynamic torque curve is an important aspect of stepping motor’s output performance. The followings are some keyword explanations. A. Working frequency point express the stepping motors rotational speed versus the drive pulse rate.n = q * Hz / (360 * D)
n: rev/sec
Hz: the frequency value or the driver pulse rate.
D:the subdividing value of motor driver
q: the step angle of stepping motor
B. Start/Stop region: the region in which a stepping motor can be directly started or stopped.
C. Slew Range: the motor cannot be started directly in this area. It must be started in the start/stop
region first and then accelerated to this area. In this area, the motor can not be directly stopped, either. Otherwise this will lead to losing-step. The motor must be decelerated back to the start/stop region before it can be stopped.
D. Maximum starting frequency point at this point, the stepping motor can reach its maximum starting speed under unloaded condition.
E. Maximum running frequency point at this point the stepping motor can reach its maximum running speed under an unloaded condition.
F. Pull-in Torque: the maximum dynamic torque value that a stepping motor can load directly at the particular operating frequency point.
G. Pull-out Torque: the maximum dynamic torque value that a stepping motor can load at the particular operating frequency point when the motor has been started. Because of the inertia of rotation the Pull-Out Torque is always larger than the Pull-In Torque.
What are the differences between PM and VR and Hybrid stepper motors?
Comparison of performance parameters of PM motor and VR, Hybrid stepping motor.Permanent Magnet vs Variable Reluctance vs Hybrid Stepper Motors
Characteristic | Permanent Magnet stepper motors | Variable Reluctance stepper motors | Hybrid stepper motors |
Cost | Cheapest | Moderate | Relatively expensive |
Design | Moderate | Simple | Complex |
Resolution | step angle: 3°~30° | step angle: 1.8°, 0.9° and smaller | step angle: 1.8°, 0.9° and smaller |
Speed Torque curve | High Torque at low speed, more pronounced torque drop at high speed | Less pronounced torque drop at high speed Noisy | High Torque at low speed, more pronounced torque drop at high speed (Maximum torque at the same speed) |
Noise | Quiet | Noisy | Quiet(quieter if using microstepping) |
Heat | Low temperature rise | High temperature rise(Need heat sink) | Low temperature rise |
Microstepping | Full, Half and Microstepping | Typically run in Full-Step only | Full, Half and Microstepping |
Rotor material | Ferrite magnet or NdFeB | Silicon steel sheet or iron(Non-permanent magnet) | NdFeB |
Technical about Rated Current
Rated current of PM stepper is limited by thermal characteristics.About Rated Current
Rated current of PM stepper is limited by thermal characteristics. In actual application, to get higher output torque we can supply with higher current, which extend rated value. In such case, the motor can't be in continuous working, otherwise the winding will be overheat even damage device. Duty cycle need to be not reach to 100%, also we must consider Max. working time - Ton Max. How to define the duty cycle with multiple of rated current How to calculate the max. Single working time with multiple of rated current Motor winding temperature rising curve8mm Permanent Magnet Stepper Motors
Miniature Permanent Magnet DC Stepper Motor, Small Size, 8mm Diameter, 2 phase, 18°
Brand:MOONS'
Item | Phase | Length (mm) |
Rated Current (A) |
Holding Torque (Nm) |
Holding Torque (mNm) |
Holding Torque (oz-in) |
Coil Type | Price (USD) |
Compare |
---|---|---|---|---|---|---|---|---|---|
8PM020S1-02001 | 2 | 8.5 | 0.25 | 4.0E-4 | 0.4 | 0.06 | Bi-Polar |
$40.00
|
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