Stepper motors are widely used in precision control systems, and the microstep drive technology is a key method to improve their performance. This technique divides each full step into multiple smaller steps, significantly enhancing the smoothness of motion and reducing vibration at low speeds. However, the impact of microstepping on angular velocity stability is not always straightforward. Understanding how microsteps affect the motor’s behavior across different frequency ranges is crucial for optimal design and application. The average speed of a stepper motor is determined by the control pulse frequency (fcp), the number of logical energization states (M), and the number of rotor teeth (Zr). The relationship can be expressed as: $$ \text{Average speed} = \frac{f_{cp}}{M \cdot Z_r} $$ or in terms of angular velocity: $$ \omega = \frac{f_{cp} \cdot 360^\circ}{M \cdot Z_r} $$ Microstep drive technology allows the motor to run with finer control over its position, which is especially beneficial at low speeds where conventional stepping often results in jerky motion. The system is divided into three main frequency domains: extremely low frequency, low frequency, and high frequency. Each domain has distinct characteristics in terms of angular velocity fluctuation and response. In the extremely low frequency range, the motor's angular velocity fluctuates significantly due to free oscillations between steps. Here, the maximum angular velocity can reach values several times higher than the average. In the low frequency range, the pulses are more frequent, but the motor still experiences residual oscillation from previous steps, leading to potential instability or resonance when the pulse frequency matches the motor's natural frequency. At high frequencies, the motor enters a continuous running state, where the angular velocity becomes more stable. The microstep drive ensures that the motor moves smoothly without the noticeable "step feel" seen in full-step mode. For example, a typical hybrid motor with 102 rotor teeth and a natural frequency of 100 Hz requires a minimum speed of around 120 rpm to operate smoothly in full-step mode. With microstepping, this threshold can be significantly reduced, allowing for smoother operation even at lower speeds. Experimental studies have shown that increasing the subdivision number reduces angular velocity fluctuations. For instance, with a subdivision number of 1024, the motor can operate smoothly at much lower speeds. However, beyond a certain point, further increases in subdivision do not yield significant improvements in stability. This suggests that while microstepping enhances performance at low speeds, it has limited benefits at higher speeds where the motor is already operating in a stable regime. Moreover, the angular velocity waveform under microstep drive shows a fourth harmonic characteristic, meaning that the fluctuations occur four times per pitch. This pattern becomes less pronounced as the subdivision number increases, leading to a more uniform motion. The study also introduced a new method to analyze microstep angle errors using angular velocity curves, offering a practical way to evaluate the performance of microstep drives. In conclusion, microstep drive technology significantly improves the stability and smoothness of stepper motors at low speeds, making it an essential feature for precision applications. However, its effectiveness diminishes at higher speeds where the motor naturally operates in a more stable range. Proper selection of the subdivision number and understanding of the frequency domains are critical for maximizing the benefits of microstep drive systems.
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