As actuators, stepper motors are favored in many fields for their simple structure, easy control, and high safety. They can deliver significant torque at low speeds without the need for gearboxes. Compared with brushless DC motors and servo motors, they enable position control without complex algorithms or encoder feedback—which is why they’re widely used in scenarios that require precise positioning. They’re also indispensable in applications needing motion control, such as automation systems, digital manufacturing (e.g., 3D printing), medical devices, and optical equipment.

  One drawback of stepper motors is their relatively high noise level, particularly at low speeds. Vibration primarily stems from two sources: the motor's step resolution (step resolution) and adverse mode responses from chopping and pulse width modulation (PWM).

  A typical stepper motor has 50 poles, equating to 200 full steps. In full-step mode, each step covers 1.8° of rotation, requiring 360° for a complete revolution. However, some stepper motors feature smaller step angles, such as those requiring 800 steps for a full rotation. Initially, these motors were operated in full-step or half-step modes, with vector currents supplied to coil A (blue) and coil B (red) in rectangular waveforms. These waveforms describe a complete 360° cycle. Figures 3 and 4 clearly show that at the 90° commutation point, the coil current is either at full power or zero.

  Low-resolution stepping modes like half-step or full-step are primary sources of stepper motor noise. They induce significant vibration within the mechanical system, particularly during low-speed operation and near mechanical resonance frequencies. At high speeds, this effect diminishes due to inertia, allowing the motor rotor to behave as a harmonic oscillator or spring pendulum.

  After the new vector current is output from the driver, the motor rotor moves to the next full or half step position according to the new position command. Similar to a pulse response around the new position point, the rotor generates overshoot and oscillations, leading to mechanical vibration and noise. To mitigate these vibrations, the concept of step subdivision was introduced. This involves dividing a full step into smaller segments or microsteps, with typical subdivision factors being 2 (half-stepping), 4 (quarter-stepping), 8, 32, or even higher.

  The current in the motor's stator coils is neither the full current nor zero, but an intermediate value. Compared to four full steps, this current profile more closely resembles a sine wave. The permanent magnet rotor position is located between two full steps (at the synthetic field position). The maximum subdivision is determined by the driver's A/D and D/A capabilities.

  TRINAMIC's drivers and controllers achieve 256 microsteps (8-bit) using integrated sinusoidal configuration tables, enabling stepper motors to achieve extremely fine angular control. Figure 6 illustrates the fluctuations when reaching a new position.

  Another source of noise and vibration stems from traditional chopping methods and pulse width modulation (PWM) modes. While coarse step resolution is a primary factor in generating vibration and noise, issues arising from chopping and PWM are often overlooked.

  The conventional constant PWM chopping mode is a current-controlled PWM chopping mode. This mode has a fixed relationship between fast decay and slow decay. The current only reaches the specified target current at its maximum value, ultimately resulting in an average current that is less than the expected target current, as shown in Figure 7.

  During a complete electrical cycle, the current direction changes at the zero-crossing point of the sine wave, creating a brief transition period where the current in the coil is zero. This results in zero torque at that moment, causing motor oscillation and vibration, particularly at low speeds.

  Compared to constant chopping mode, TRINAMIC's SpreadCycle PWM chopping mode automatically configures a hysteresis decay function between slow and fast decayers. The average current reflects the configured nominal current, eliminating the transition period at the sine wave zero-crossing point. This reduces current and torque fluctuations, resulting in a current waveform closer to a sine wave. Compared to traditional constant chopping modes, motors controlled by SpreadCycle PWM operate significantly smoother and more stable.

  This is particularly crucial during motor acceleration from standstill or low speeds to medium speeds.

  How to Achieve Completely Silent Stepper Motor Operation?

Stepper motors, especially at low speeds, generate noise primarily from low-resolution stepping modes like half-step or full-step operation. Another significant source stems from poor chopping and pulse width modulation (PWM) mode responses.

  Noise Reduction Secret #1: Microstepping Drive

  Stepper motors operate by “generating a magnetic field through energized coils to drive the permanent magnet rotor.” The applied current must undergo “chopping” regulation to ensure the rotor operates as required.

  Hybrid stepper motors fundamentally operate at 200 steps per revolution. Utilizing additional current states to achieve “half-step” or “microstep” modes enhances precision, torque, and efficiency while reducing lost steps, vibration, and noise.

  Noise Reduction Secret #2: SpreadCycle™

  Another source of stepper motor noise and vibration stems from traditional chopping methods and pulse width modulation (PWM) modes. While coarse step resolution is a primary factor in generating vibration and noise, we often overlook issues introduced by chopping and PWM. Traditional constant PWM chopping employs current-controlled PWM chopping, featuring a fixed relationship between fast and slow decay phases. Current only reaches the specified target value at its maximum point, resulting in an average current below the intended target.

  Compared to constant chopping, ADI Trinamic's SpreadCycle PWM chopping automatically configures a hysteresis decay function between slow and fast decay phases. The average current reflects the configured nominal current, eliminating transition periods at sine wave zero crossings. This reduces current and torque fluctuations, resulting in a more sinusoidal current waveform. Compared to traditional constant chopping modes, motors controlled by SpreadCycle PWM operate significantly smoother and quieter, achieving silent motor control.

  Noise Reduction Secret #3: StealthChop™

  While advanced current-controlled PWM choppers improve motor performance, noise and vibration remain critical issues for certain applications. This stems from current-regulated choppers reacting to coil current measurements on a cycle-by-cycle basis, generating noise and electromagnetic coupling between motor coils that affects the current chopper. The StealthChop™ voltage-regulated chopper overcomes this by modulating current based on PWM duty cycle, generating a perfect current sine wave.

  Except for the unavoidable friction noise from motor bearing balls, StealthChop enables motors to operate in extreme silence, controlling motor sound below 10dB—significantly quieter than traditional current-controlled methods.