Holding torque, also known as static torque, refers to the rotational force that the stator exerts on the rotor when the stepper motor is energized but not moving. This torque is crucial because it determines the motor’s ability to hold a position under load. At low speeds, the motor's torque is close to the holding torque, but as speed increases, the torque drops rapidly, which affects the output power. Therefore, holding torque is one of the most important parameters for evaluating a stepper motor's load capacity.
First, consider the holding torque. It represents the maximum torque the motor can exert without rotating. For example, a motor rated at 1N.m typically means its holding torque is 1N.m. This value is essential when selecting a motor for applications where stability and precision are required.
Second, choose the number of phases. Two-phase motors are cost-effective but have larger step angles (at least 1.8°), higher vibration at low speeds, and less efficiency at high speeds. They are suitable for applications where speed is more important than precision. Three-phase motors offer smaller step angles (at least 1.2°), reduced vibration, and better low-speed performance. Their maximum speed is 30–50% higher than two-phase motors, making them ideal for applications requiring accuracy and stability. Five-phase motors provide even finer steps and better low-speed performance but come at a higher cost, suitable for high-precision tasks.
Third, select the motor based on application needs. Always determine the load characteristics first before choosing a driver. Compare the static torque and torque-frequency curves of different motor types to find the best match. When high accuracy is needed, use mechanical reduction to operate the motor efficiently and quietly. Avoid operating in vibration zones by adjusting voltage, current, or adding damping if necessary. For power supply, DC voltages between 24V and 36V are generally recommended. Larger motors like 86-series require 46V, while 110-series need over 80V. For high inertia loads, select a motor with a larger frame size. If high inertia and speed are involved, gradually increase the frequency to prevent stepping out, reduce noise, and improve positioning accuracy when stopping. Stepper motors typically have torque below 40Nm; for higher torque or speeds above 1000RPM, consider servo motors. AC servos can run up to 3000RPM, while DC servos can reach 10,000RPM.
Fourth, choose the driver and subdivision settings. Avoid full-step mode due to increased vibration. Opt for a driver with lower current, higher inductance, and lower voltage if possible. Use a driver with higher current rating than the motor's working current. For low vibration or high precision, use a subdivision driver. High-voltage drivers are ideal for high-torque motors to achieve better high-speed performance. If the motor runs at high speed with low precision, avoid high subdivision settings to save costs. For low-speed applications, use high subdivision to ensure smooth operation and reduce noise. In short, the subdivision setting should be chosen based on actual motor speed, load torque, gear ratios, accuracy requirements, and noise levels.
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