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Analysis of three working states of stepper motor
The behavior of a step-and-drag motion is largely influenced by the drive system, mechanical design, and the characteristics of the stepper motor itself. Understanding how the motor operates under different conditions is essential for optimizing performance and avoiding issues like missed steps or overheating.
A stepper motor can operate in three main states: static, steady-state, and transient (or transition) state.
In the **static state**, the rotor is momentarily locked in place. This occurs when a DC current is applied to the windings, with no pulse signal (frequency f=0). At this point, the motor's phase current reaches its maximum, and the rotor remains stationary. Since the windings are not being reloaded, heat is generated unevenly in the active phase, which can lead to significant thermal stress. This condition is one of the most critical and must be carefully managed to avoid damage.
In the **steady-state** operation, the motor runs at a constant speed, synchronized with the control pulse frequency. This state can be further divided into two types: limit (continuous frequency) and non-limit. The **limit synchronization state** occurs when the motor is operating at its maximum pulse frequency (fmax) under a given load. At this frequency, the rotor rotates smoothly without oscillation. However, this state requires specific starting procedures; if the frequency exceeds fmax, the motor will lose synchronization, leading to step-out.
When the frequency is below fmax, the motor enters a **non-limit steady-state**, where the rotor may experience stable oscillations. These oscillations are particularly problematic near resonant frequencies, as they can cause instability and reduce the motor’s efficiency.
In the **transient state**, the motor undergoes changes in speed or direction. For example:
1. When the frequency suddenly increases from zero to a starting frequency (fq), the rotor accelerates to the maximum speed. If the frequency exceeds fq, the motor cannot start properly and may lose steps.
2. If the control pulses are abruptly stopped, the motor decelerates to a locked position. This process depends on the braking frequency (fs), and above this value, a smooth stop is not possible.
3. Reversing the motor involves changing the winding sequence, causing the rotor to switch between two stable synchronous states. There is a **limit inversion frequency (ft)**, and exceeding it can result in missteps.
These operations—starting, stopping, and reversing—can occur under various initial conditions, such as different angular positions (θ) and speeds (η). However, these initial conditions significantly affect the values of fq, fs, and ft, making the calculation of drag more complex. Therefore, during motor design and selection, it's crucial to consider the initial conditions and ensure that the motor can handle the expected operational scenarios. Additionally, when testing or selecting a motor, it's important to have detailed knowledge of the experimental conditions, including the initial setup and data collection methods.