To operate within the range between the pull-in and pullout regions, the stepper motor must initially start in the start/stop region. The pulse rate is then progressively increased until the desired speed is achieved. Conversely, to stop the stepper motor, the speed is gradually reduced until it falls below the pull-in torque curve.
Torque is directly proportional to the current flowing through the stepper motor windings and the number of wire turns. If there is a need to increase the torque by 20%, it is advisable to raise the current by approximately 20%. Similarly, if a decrease in torque by 50% is desired, reducing the current by 50% would be appropriate.
However, it is important to consider magnetic saturation, as exceeding 2 times the rated current does not yield any additional increase in torque. Beyond this point, further increasing the current will not provide any benefit. Moreover, pushing the current to around 10 times the rated value carries the risk of demagnetizing the rotor.
All our stepper motors are equipped with Class B insulation, which can withstand temperatures up to 130°C before the insulation starts to degrade. To maintain safe operating conditions, it is recommended to maintain a temperature differential of 30°, ensuring that the motor case does not exceed 100°C.
The inductance of the stepper motor has an impact on high-speed torque performance. Inductance arises from the inherent characteristics of the stepper motor windings, comprising a combination of inductance and resistance. The ratio of inductance in henrys to resistance in ohms yields a value expressed in seconds. This value represents the time constant, indicating how long it takes for the coil to charge up to 63% of its rated value. For example, if the stepper motor is rated for 1 amp, after 1 time constant, the coil will reach approximately 0.63 amps. After approximately 4 or 5 time constants, the coil will charge up to 1 amp. Since torque is directly proportional to current, if the current is only charged up to 63%, the motor will exhibit approximately 63% of its maximum torque after 1 time constant.
At lower speeds, the stepper motor operates without any significant issues. The current can flow in and out of the coils at a sufficient pace, allowing the stepper motor to generate its rated torque. However, as the speed increases, a challenge arises. The current is unable to enter the coils quickly enough before the next phase is switched. As a result, the torque output of the stepper motor is diminished.
The voltage supplied by the driver significantly influences the high-speed performance of the stepper motor. A higher ratio of drive voltage to motor voltage leads to improved performance at high speeds. When operating with higher voltages, the current is forced into the motor windings at a faster rate compared to the 63% mentioned earlier.