Closed-Loop Technology Stepper motors Functionality Closed-loop stepper motors combine the advantages of both stepper and servo motor technologies. They operate smoothly with reduced resonance, provide precise position feedback and control, offer short settling times, and eliminate step loss entirely. These motors are an excellent alternative to traditional stepper motors when energy efficiency, quiet operation, and high load tolerance are priorities. Compared to servo motors, closed-loop steppers provide high torque at low speeds, rapid settling, accurate positioning without back swing, and a cost-effective solution – often in smaller, more compact sizes. The closed-loop method, also known as sine commutation with an encoder using field-oriented control, relies on performance-optimized current control and precise feedback of encoder signals. The encoder monitors the rotor’s position, allowing the system to generate sinusoidal phase currents in the motor windings. Vector control keeps the stator’s magnetic field perpendicular to the rotor’s, and precisely matches its field strength to the required torque. By controlling the current in the windings, the motor produces a uniform force, resulting in exceptionally smooth operation and highly accurate control. True vs. pseudo closed loop Some stepper motors appear to be closed-loop because they use encoders, but they lack field-oriented control with sine-commutated current. These motors only monitor step position and cannot correct step angle errors during operation. In contrast, a true closed-loop system with field-oriented control actively compensates for step angle errors during motion and corrects load angle deviations within each full step, ensuring precise and reliable performance. Advantages over standard stepper motors Classic stepper motors are reliable and cost-effective drives ideal for moving to predefined positions. They operate in clock-direction, or open-loop mode, meaning control signals are not fed back. The absence of position feedback is a limitation, as step offsets or step losses caused by overload cannot be detected. Additionally, lower operating frequencies can increase resonance, and even a slight load increase or torque spike may cause the motor to lose steps, fall out of synchronization, or stop entirely. Closed-loop stepper motors represent an evolution of classical stepper technology, overcoming many of their traditional limitations:No need to calculate or purchase a large safety margin (often up to 50%)Consistent performance under load fluctuations, with no stoppage on overloadEnergy-efficient operation through intelligent current controlPractically resonance-free operationLonger bearing life thanks to reduced heat and vibrationShorter acceleration times, as high torque is maintained even at elevated speedsAccurate positioning through continuous monitoring and correction Advantages over servo motors Closed-loop stepper motors from Nanotec are often a practical alternative to servo drives, particularly in applications such as winding or conveyor belt systems. They provide precise control of rotational speed, position, and torque – critical in torque-driven processes like winding. By combining the strengths of both stepper and servo technology, these motors deliver high maximum torque, excellent efficiency, optimal dynamics, minimal torque ripple, and exceptionally quiet operation. In torque mode, the closed-loop stepper motor behaves like a spring, with the spring characteristics adjustable via a potentiometer. The motor provides a stable force even when resisting an opposing load while stationary. As the opposing force decreases, the motor rotates and adjusts its torque proportionally up to the set current or torque limit. This makes the closed-loop stepper motor ideal for winding, tensioning, and pressing applications. Closed-loop stepper motors are an ideal choice for applications that require:High torque at speeds of up to 500 rpm, providing a compact and cost-effective solution without a gearboxFast commissioning without complex or expensive tuningThe ability to hold a load in position while at standstillThe avoidance of transient and free oscillations (hunting) typical of servo motors, which can occur with variable loads or pulsations and lead to unacceptable following errors. On sudden load changes, servo motors may lose position and require correction.Ideal application areas:Multiple-axis systems (serial, Ethernet, EtherCAT, CANopen)Positioning tasks involving variable loadsWinding applicationsBelt drives with start/stop and precise positioning requirementsDosing pumps and filling systemsSemiconductor assemblyWafer productionTextile machinery and industrial sewing machinesRoboticsTesting and inspection systemsApplications demanding smooth operation, short settling times and precise positioning
