Optimizing Stepper Motors with Microstepping
Microstepping increases the accuracy, torque, energy efficiency, and smoothness of stepper motor applications while at the same time reducing step loss, vibrations, and noise. Stepper motor drives can be controlled with a sinusoidal current waveform by dividing full steps into smaller microsteps to achieve the utmost precision and smooth movement. With up to 256 microsteps per full step, ADI Trinamic™ technology transforms digital information into perfect physical motion. The resulting current control scheme reduces noise and vibrations while increasing the accessible torque and precision.
How Stepper Motors Work
Stepper motors are durable open-loop motors that offer several advantages over other electric motors: they have high torque at low speeds and standstill; their marginal positioning error is noncumulative; they have an excellent response to start/stop; they’re cost-efficient and easy to use also. This makes stepper motors an advantageous choice when precise and reliable open-loop positioning is needed. Stepper motors operate by sending an electrical current through the motor coils to create an electromagnetic field that forces the magnetic rotor into the desired position. This can be done in full steps, half steps, or smaller microsteps using additional current states.
The Microstepping Difference
Mechanically, a stepper motor is similar to a mass-spring system. When moving from one position to another, the rotor doesn’t immediately find the right position. Instead, it will overshoot and oscillate around the target position until it reaches it. And just like with a mass-spring system, the larger the difference from one position to the next, the larger the oscillation.
Microstepping aims to drive motors with a current waveform that’s sinusoidal. This means the stator coils are not powered with either full or zero current but with intermediate current levels approximating a complete sine wave shape over four full steps. This positions the permanent magnet rotor in intermediate positions in between two subsequent full steps. Microstepping further allows for custom current waveforms adapted to the stepper motor’s physics or application. The maximum microstep resolution is defined by the driver electronic’s A/D and D/A capabilities.
When adapted to a hybrid stepper motor, the ADI Trinamic 256× microstepping technology provides 51,200 microsteps per full 360° revolutions. That’s an accuracy of up to 0.00703125° per full revolution.
Oscilloscope shot of fullstepping
Oscilloscope shot of microstepping
Getting Systems in Step with ADI’s Microstep Interpolator
The motion controllers integrated into the ADI Trinamic cDriver™ products leverage microstepping technology, as do the motion control ICs and driver ICs that offer the 256-microstep resolution. In fact, microstepping is a standard feature for all ADI Trinamic products, but not every motion control system on the market offers such high step resolution. The ADI Trinamic MicroPlyer™ interpolator adds current steps between step pulses while preserving position and velocity. This enables any motor control system to operate at a 256-microstep resolution, delivering industry-leading stepper motor control without requiring a full system upgrade.
