Stepper motor, an executive element, is one of the key products of mechatronics and is widely used in a variety of automated control systems. As microelectronics and computer technology develop rapidly, there’s an increasing demand for stepper motors in various fields. Everyone in the electricity industry should manage to have a more in-depth understanding of its structure, working principles and applications. Here high quality stepper motor factory Leili Motor introduces a stepper motor in a comprehensive manner in terms of three aspects.
What is a stepper motor?
A stepper motor, also known as step motor or stepping motor, is a kind of electromechanical device that directly converts electrical pulses into mechanical movement. The controlling of the sequence, frequency and number of electrical pulses applied to the motor coils can help control its steering, speed and rotation angle. A best step motor and its accompanying driver constitute a simply controlled and low-cost open-loop control system, which can achieve accurate position and speed control, requiring no closed-loop feedback control system with position sensing. A stepper motor mainly consists of front end cover, bearing, center shaft, rotor core, magnet, winding insulation, stator core, curved washer, rear end cover, and screw.
What is the working principle of a stepper motor?
The stepper motor driver controls the winding to be energized in certain timing sequence in forward or reverse direction according to external control pulses and direction signals through its internal logic circuit, making the motor rotate forward/reverse or lock.
For a 1.8 degree two-phase stepper motor, when the windings of twp phases are energized and excited, the motor output shaft will be stationary and locked in position. The maximum torque that keeps the motor locked at the rated current is the holding torque. If the current of the winding in one of the phases changes its direction, the motor will rotate by one-quarter pitch (1.8°) in a given direction, according to study from step motor suppliers; if the current of the winding in another phase is redirected, the motor will rotate by one-quarter pitch (1.8°) in the opposite direction. When the currents passing through the coil winding are sequentially redirected to excitation, the motor will continuously rotate accurately in the given direction.
Two-phase best step motors are available in two basic winding types: bipolar and unipolar. A bipolar motor has a single winding coil per phase, and rotates continuously with the current in the same coil to be excited in sequence, so the high quality stepper motor factory should design the drive circuit with eight electronic switches for sequential switching. Unipolar motors have two winding coils of opposite polarity on each phase, and rotate continuously by alternately energizing the two winding coils on the same phase. Only four electronic switches are needed for the design of the drive circuit. The output torque of the motor is increased by about 40% in the bipolar drive mode compared to the unipolar drive mode because the winding coils of each phase are 100% excited.
What are technical features of stepper motors?
A. Load torque (Tf). Tf = G * r. G: load weight; r: radius
B. Inertia torque (TJ). TJ = J * dw/dt. J = M * (R12+R22) / 2 (Kg * cm). M: load mass; R1: outer radius; R2: inner radius; dω/dt: angular acceleration
2. Speed-torque curve
Step motor suppliers find the speed-torque curve is an important expression of the output characteristics of a stepper motor.
A. Operating frequency: rotation speed at a point.
n = q * Hz / (360 * D). n: rev/s; Hz: frequency; D: drive circuit fraction value; q: step angle
For a stepper motor with a step angle of 1.8° has a speed of 1.25r/s at an operating frequency of 500Hz for a 1/2-fraction drive (i.e. 0.9° per step).
B. Self-starting area: the area where stepper motors can start and stop directly.
C. Continuous operation area: the motor cannot be started or stopped directly in this area. The best step motor must first pass through the self-starting area and then accelerate to this area. In addition, the motor cannot be braked directly in this area, otherwise it will easily stall, so it must first be decelerated to the self-starting area before braking.
D. Maximum starting frequency: the maximum pulse frequency at which the motor can run without losing step under no load.
E. Maximum operating frequency: the maximum pulse frequency at which an excited motor can run without losing step under no load.
F. Starting torque/traction torque: the maximum load torque of the stepper motor to start and operate at a certain pulse frequency without losing step.
G. Operation torque/prevailing torque: the maximum load torque of the stepper motor under a certain pulse frequency and stable operation without losing step.
3. Vibration and noise
In general, when the motor operating frequency is close to or equal to the motor rotor’s intrinsic frequency, the stepper motor in no-load operation will resonate and even lose steps. Step motor suppliers offer two solutions for resonance. (1) Avoid the vibration zone, to prevent the motor’s operating frequency falling within the vibration range. (2) Adopt fraction drive mode: Use micro-step drive mode to reduce vibration by subdividing the original one step into multiple steps to increase the resolution of each step. This can be achieved by adjusting the phase to current ratio of the motor. Microstepping does not increase the step angle accuracy, but makes the motor run more smoothly and with less noise. The torque is generally 15% lower for half-step operation than for full-step operation, and 30% lower for sine wave current control.
4. Acceleration/deceleration control
When the operating frequency point of best step motor is in the continuous operation area of the speed-torque curve, it is crucial to shorten the acceleration or deceleration time when starting or stopping the motor, so that the motor can run at the optimal speed for a longer period of time, thus increasing the effective running time of the motor.
Post time: Apr-29-2022